No.1 seed Ashleigh Barty extended her winning streak at the Miami Open to eight after winning a clash of former Roland Garros champions 6-3, 6-2 over Jelena Ostapenko.

The defending champion had toiled for nearly two-and-a-half hours against qualifier Kristina Kucova in her opener, needing to save a match point, but was much more solid against Ostapenko. Barty tallied nine winners to 14 unforced errors, and responded to dropping serve for the only time by reeling off the last six games of the match from 0-2 down in the second set.

"Today felt like I was a lot sharper and switched on and ready to go from the very first point," Barty said afterwards. Deploying her slice in backhand-to-backhand exchanges successfully elicited a number of errors from Ostapenko, who racked up 32 in total to 15 winners.

The Australian also came out on top of the three longest games of the match, all of which were key in terms of scoreboard momentum. Ostapenko held four break points in the very first game, but ultimately conceded it with consecutive backhand errors. She fired several stunning winners to save five set points as Barty served for the first set, only for the World No.1 to wrap up her sixth with a service winner. And having broken Barty at the start of the second set, Ostapenko netted a backhand after a two-deuce tussle for the immediate break back.

"The goal today was to try to bring the tennis back to my kind of tempo and my kind of rhythm as often as possible and as quickly as possible in points," Barty said.

"She obviously has the ability to take that away from you quite quickly, particularly off serve and first shot and off her returns. So it was about being patient at times and making sure we tried our best to neutralize and then bring the game back in our favor."

Meanwhile, wildcard Ana Konjuh's comeback from her fourth elbow surgery gathered even more momentum as the Croat upset No.15 seed Iga Swiatek 6-4, 2-6, 6-2 in 2 hours and 14 minutes.

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Known for her formidable power as a teenager, Konjuh has now defeated two of the hardest hitters on the current tour in consecutive matches, following her second-round upset of No.18 seed Madison Keys. The former World No.20 was able to soak up Swiatek's pace to create a series of winning shots from every corner of the court, striking 40 winners to the reigning Roland Garros champion's 27.

That was particularly the case in a brilliant first set in which Konjuh committed a meagre three unforced errors (out of 18 in total). Her level dipped in the second set as Swiatek fought back, but Konjuh emerged for the decider with renewed energy.

Stepping in to attack Swiatek's serve paid dividends as Konjuh broke the Pole twice, while improved serving saw her ace count rise to 10. The World No.338 did not face a break point throughout the third set, and closed out the win with a one-two punch.

The result marks the first time Konjuh has won three consecutive WTA main Β draw matches since her run to the 2017 Wimbledon fourth round, and the first time she has defeated Top 20 players in back-to-back matches since beating Samantha Stosur and Elena Vesnina at Dubai 2017. Perhaps surprisingly, Konjuh had not won a main draw match in Miami prior to this year, losing her 2017 opener to Kirsten Flipkens in her only previous appearance.

Afterwards, Konjuh said that she was most proud of her "fighting spirit".

"I knew it was going to be tough," she said. "I just told myself I need to stay and be offensive and not give her many chances. That second set maybe I screwed up a little bit, but overall, credit to her. You know, she stepped up her game. But I just wanted to stay mentally in it in those key moments just to be able to, you know, produce some great shots. I did that."

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Konjuh's ability to produce phenomenal winners is familiar to anyone who watched her reach the 2016 US Open quarterfinals as an 18-year-old. It has not been dimmed, but she is now using it in a different way.

"My coach is with me, and he's just trying to produce this new level of my game," she said. "Not being as offensive but also being smart about it and not going for the killer shots at the moments that are not there."

It's a more thoughtful attitude which now informs her approach to the whole sport.

"When I was still in the top and playing, I was like, 17, 18? Just never knew what I'm going to go through and suffer through. But at the time I didn't know better. I was always winning and always moving forward. So I don't think that I appreciated the game as much as I do right now. I was playing more on instinct than just thinking about it.

"Compared to now where I'm actually maybe overthinking things, which is not a good point, but also just being aware of everything on court. Having been through what I have been through, it just gives me much more strength and much more just will and power to keep pushing. I don't want to quit. I don't want to give up. I think that's a good thing."

Up next for Konjuh with a quarterfinal berth at stake will be the unseeded Anastasija Sevastova. The former US Open semifinalist advanced to the fourth round after No.3 seed Simona Halep withdrew due to a right shoulder injury.

"I'm very sorry I have to pull out of singles and doubles at the Miami Open, but my injury doesn't let me play here as expected," Halep said in a statement.

"I'm sad that I can't continue, I wanted to come here to give my best and play many matches but unfortunately I can't. Hopefully next year I will be back healthy and better."

In the first clash between seeded players, No.5 Elina Svitolina held off No.30 Ekaterina Alexandrova 7-6(1), 6-4, extending her record against the Russian to 3-0.

It was a masterful scoreboard performance from Svitolina, who found herself continually pegged back by Alexandrova. The Ukrainian twice lost a break lead in the first set, including failing to serve it out at 5-4. But, suddenly trailing 5-6, Svitolina gathered her focus and reeled off 10 straight points to take a commanding tiebreak lead.

In the second set, Alexandrova battled from 1-3 down to level at 3-3 after breaking back in an extended tussle. However, Svitolina once again struck at the tail end of the set, capturing the Alexandrova serve to take victory on her opponent's eighth double fault of the day.