Simona Halep, Venus Williams are ousted at US Open

“I feel like a little kid, like this is the first time ever happening,’’ Lucic-Baroni said.

Lucic-Baroni won with two straight aces.

‘‘It was really easy,’’ she said through tears later. ‘‘Right now it’s hard.’’

Hard thinking back to the 15 years since she last made a Grand Slam round of 16. The days spent working out wondering if she’d find the financial backing to return to competition. The injuries that would crop up just as she was regaining her form.

She kept going, kept running herself breathless in practice, kept grinding through minor-league tournaments — all for a moment like Friday.

She was 17 when she reached the 1999 Wimbledon semifinals. Lucic-Baroni, who won the 1998 Australian Open doubles title with Martina Hingis, was a prodigy: At her very first WTA event as a 15-year-old, she won. That year, she made it to the third round at the US Open.

Like many tennis aficionados, Lucic-Baroni watched 15-year-old CiCi Bellis play her second-round match Thursday. The Croatian veteran was charmed by the youngster’s wide-eyed delight. She also couldn’t help but contrast that to herself at the same age.

‘‘I was feeling like an adult at 15 when I played here,’’ Lucic-Baroni said. ‘‘She’s just a little girl.’’

It’s as though Lucic-Baroni is living her life in reverse — stoic as a teen, childlike as a 30-something.

‘‘I was so young and I was so good and I was winning so much that, even though it’s exciting, it wasn’t really a big deal,’’ she said. ‘‘It was just a natural progression.’’

Now, she added, ‘‘Every round is amazing.’’

‘‘In a way, I know I sound like and I feel like a little kid, like this is the first time ever happening,’’ she said. ‘‘I love the feeling.’’

She didn’t play a Grand Slam match for nearly eight years, from the 2002 US Open through 2010 Wimbledon.

‘‘When I would get my chance on a big court against a big player, I wanted it so bad that I kind of was paralyzed,’’ she said.

She'd fret: ‘‘OK, how many more do I have? I have to do it now.’’

Finally she relaxed and told herself: ‘‘Just play tennis.’’

But in Doha in February, her back gave out against Agnieszka Radwanska. At Indian Wells the next month, she had a bulging disk in her neck.

She was on an eight-match losing streak coming into US Open qualifying and trailed, 4-2, in the third set of her first match. Then in her last match, Lucic-Baroni was down 5-2 in the third, two points from defeat, with her opponent serving to clinch the spot in the main draw.

By comparison, facing three set points Friday against the French Open runner-up seemed less daunting. With Halep trying to serve out the first set at 5-2, Lucic-Baroni broke back after five deuces. Halep started unraveling, and Lucic-Baroni started rolling.

‘‘Everything was in for her,’’ Halep said.

For years, coaches tried to change Lucic-Baroni’s aggressive style. She said she’s playing much better now that she’s ‘‘starting to feel like myself again finally.’’

‘‘I'm not the type of player that builds points and loops balls and kind of waits for their opportunities,’’ she said with a laugh.

‘‘I enjoy hitting winners,’’ she added. ‘‘I enjoy hitting aces.’’

Lucic-Baroni had only once before defeated a top-five opponent — that happened during the 1999 Wimbledon run, against Monica Seles.

‘‘I feel fit. I feel strong in my mind,’’ Lucic-Baroni said. ‘‘I feel very excited, even after so many years on tour.’’

She got married in November 2011 and said ‘‘I would be perfectly fine having a family.’’

‘‘I don’t need to do this, you know,’’ she said. ‘‘But people don’t realize how much I want this and how hard I worked for this.’’

Lucic-Baroni will next face 13th-seeded Sara Errani, who rallied to force a third-set tiebreaker and outlasted Venus Williams, 6-0, 0-6, 7-6 (7-5).

Errani wagged her finger and cupped her hand to her ear for the Open fans who tried to will Williams to victory.

‘‘I think I will remember forever that moment,’’ Errani said.

Two points from defeat, the diminutive Italian rallied after Williams had a chance to serve out the match in the final set.

Williams twice came back from down a break in the third but was done in by too many unforced errors — she made 52 in all. Trying to close out the match at 5-3, the 19th-seeded Williams had one of her eight double-faults.

Errani, who wasn’t thrilled with fans yelling out support for her opponent during her serves, won just 12 games in three previous meetings with Williams. But in the first set, Williams couldn’t take advantage of her power, making just 30 percent of her first serves.

Errani used her quickness to run Williams around the court, and she seemed sluggish after playing a long doubles match with her sister on Thursday night. But in the second, Williams, 34, looked like the seven-time major champion she is, pouncing on Errani’s soft serves.

‘‘She’s playing unbelievable,’’ Errani said. ‘‘I really don’t know how I won today.’’

Errani just had a little more left in the final set. And in the tiebreaker, Williams made four more unforced errors.

Errani’s quick reflexes, honed in doubles, gave her match point when she stabbed a backhand volley to return what looked like a sure winner by Williams.

‘‘Unbelievable,’’ Errani said. ‘‘If I don’t do that, maybe I lose.’’

After losing to Errani, Williams went on court again for doubles and won that one, although she was treated by a trainer.

Williams did not blame injury or fatigue for the way she failed to close out Errani, including getting broken while serving at 5-3 in the third.

‘‘I went for too much,’’ explained Williams, 3-0 against Errani until Friday.

The 5-foot-4½-inch Errani — 8½ inches shorter than Williams — reached the final at the French Open and the semis at the US Open in 2012, but both times she was routed by power players: Maria Sharapova and Serena Williams.

Sixth-seeded Angelique Kerber also was upset, losing, 6-1, 7-5, to Swiss teen Belinda Bencic. Bencic, 17, is coached by Hingis’s mother, Melanie Molitor, and was coming off a third-round showing at Wimbledon.

‘‘I started believing that I can play with these players,’’ Bencic said.

Maria Sharapova reached the fourth round by taking five of the last six games after Sabine Lisicki was warned by the chair umpire about receiving coaching help.

Avoiding the sort of surprise that saw half of the top eight seeded women lose already, No. 5 Sharapova eliminated No. 26 Lisicki, 6-2, 6-4, in a hard-hitting match that ended past midnight Saturday.

Sharapova trailed in the second set, 3-1, but she turned things around as Lisicki went back and forth with chair umpire Carlos Ramos over whether she was getting instructions from her entourage.

In the preceding match, second-seeded Roger Federer beat 104th-ranked Sam Groth, 6-4, 6-4, 6-4, improving to 24-1 at night in Arthur Ashe Stadium.

Federer is also 54-1 in second-round Grand Slam matches; the only loss came at Wimbledon last year.

‘‘I was trying not to get caught up in the whole ‘Roger act’ out there. You walk out, you get a few cheers. He walks out and the crowd goes ballistic,’’ Australia’s Groth said. ‘‘So from the word ‘Go,’ you know he’s there.’’

Doing an impressive job of handling the 104th-ranked Groth’s powerful serves, Federer limited him to eight aces and broke him five times.

During his on-court interview, Federer was asked about dealing with such fast-moving serves and he said, kiddingly, ‘‘My arm’s still vibrating a little bit.’’

Federer also produced a highlight-reel shot in the second set’s final game, closing a 17-stroke exchange by sliding to his backhand side, stretching and flicking a high-arching lob that landed in. Federer raised his right hand overhead and wagged his index finger in a ‘‘No. 1’’ gesture.

‘‘I knew I was playing Roger Federer,’’ Groth said. ‘‘I was pretty nervous probably all day.’’

Federer next faces 42d-ranked Marcel Granollers.

Earlier, Peng Shuai again beat a seeded player to reach her second straight Grand Slam round of 16. Two days after upsetting fourth-seeded Agnieszka Radwanska, Peng defeated 28th-seeded Roberta Vinci, 6-4, 6-3.

The Chinese veteran had gone two years without making it past the second round at a major before her Wimbledon run this summer. But she didn’t meet any seeded players in the first three rounds there before losing to eventual champion Petra Kvitova in straight sets.

This time, Peng, ranked 39th, will face 14th-seeded Lucie Safarova to try to reach her first Grand Slam quarterfinal.

Vinci, 31, had made the US Open quarterfinals the past two years, but lost in the opening round at the first three major tournaments of 2014.

Ninth-seeded Jelena Jankovic advanced by routing Johanna Larsson, 6-1, 6-0. The 96th-ranked Larsson had upset Sloane Stephens in the second round.

Half of the top eight seeds are now gone on the women’s side. Nothing like that among the men.

Eleventh-seeded Ernests Gulbis became the first man in the top 20 to lose when he blew a two-set lead to Dominic Thiem. The 20-year-old Thiem won, 4-6, 3-6, 6-4, 6-3, 6-3, to reach his first Grand Slam third round.

Sixth-seeded Tomas Berdych was pushed to five sets by 65th-ranked Martin Klizan before winning, 6-3, 4-6, 6-2, 3-6, 6-3.

Fourth-seeded David Ferrer advanced when Bernard Tomic withdrew because of a left hip injury. Seventh-seeded Grigor Dimitrov and 12th-seeded Richard Gasquet both moved on in straight sets.