INDIAN WELLS, Calif. -- Jannik Sinner defeated Jiri Lehecka 6-3, 6-3 to reach the semifinals of the BNP Paribas Open on Thursday, running his winning streak to 16 consecutive matches this year.

Sinner's streak includes the Australian Open title he won in January. The Italian is 19-0 overall dating to last year's Davis Cup. He's won 21 of his last 22 sets.

"You earned these things by working hard and believing," Sinner said in a Tennis Channel interview. "I'm just glad to be in this equation. It doesn't matter if you're 16-0 or whatever."

Sinner made just four unforced errors in the first set when Lehecka had 17 miscues.

Sinner got the lone break in the second set in the fourth game with a backhand winner. Lehecka erased Sinner's first match point in the eighth game before Sinner converted his fourth match point in serving it out.

"I've improved many things which makes me more confident on the court," Sinner said.

Top-ranked Iga Swiatek rallied from a 1-4 deficit in the first set and advanced when Caroline Wozniacki had to quit their quarterfinal.

Swiatek was leading 6-4 and had just broken Wozniacki to open the second set when the Dane retired because of a right foot issue. She had jammed a toenail on her foot earlier in the tournament and had a trainer retape it between sets.

Wozniacki, the 2011 tournament champion and former world No. 1, raced to a 4-1 lead in the first when Swiatek committed many of her 17 unforced errors.

But Swiatek turned it on from there, winning the final five games to take the first set. She broke Wozniacki in a four-deuce game to close out the set in which Swiatek had 17 winners in front of actor Will Ferrell.

Swiatek moved on to the semifinals for the third straight year in the Southern California desert, having dropped just 14 games in her matches so far. Wozniacki was in the seventh tournament of her comeback since retiring 3 1/2 years ago, marrying and having two children.

Marta Kostyuk of Ukraine defeated Russian Anastasia Potapova 6-0, 7-5 for the first time in three career meetings to reach the semifinals.

All eight quarterfinals were being played on the same day for the first time at the combined ATP Tour and WTA Tour event.