NEW YORK (AP) At 4-all in the opening set of her U.S. Open quarterfinal Tuesday, Angelique Kerber noticed the loud roar of a jet flying past. She missed a shot, lost that point, glared overhead - then followed with a trio of unforced errors to get broken.
In the past, that sequence might have been her undoing. The distraction. The deficit. The opponent outplaying her. Not now, though. Kerber's game has improved, sure, and so has her attitude. On this afternoon, she wouldn't drop another game.
Making a push to move up from No. 2 in the rankings, and to earn a second Grand Slam title of 2016, Kerber moved into the semifinals at Flushing Meadows by taking the last nine games in a 7-5, 6-0 victory over Roberta Vinci, last year's runner-up.
''I know that I can beat everybody,'' Kerber said, ''and this is what gives me also a lot of confidence and motivation.''
She has a chance to overtake Serena Williams at No. 1 after the tournament and moved into her third major semifinal of the year, which will be played Thursday against Caroline Wozniacki, a two-time U.S. Open runner-up who advanced with a 6-0, 6-2 victory over an Anastasija Sevastova of Latvia.
Sevastova twisted her right ankle on the first point of the second game and was unable to move properly the rest of the way against Wozniacki, a former No. 1 who is now ranked only 74th and hadn't won a Grand Slam match in 2016 until last week.
It's the fifth trip to the semifinals at Flushing Meadows for Wozniacki, who lost the 2009 final to Kim Clijsters and the 2014 final to her good friend Williams.
Kerber beat Williams in the Australian Open final this January, then lost to Williams in the Wimbledon final in July.
''In tough moments,'' Vinci said about Kerber, ''the mind is important.''
In 2015, Vinci reached her first major final by stunning Williams to end the American's bid for the first calendar-year Grand Slam in tennis in more than a quarter-century.
But after being two points from taking the first set against Kerber while serving for it at 5-4, 30-all, the No. 7-seeded Vinci faltered badly. She missed a forehand long, then netted a backhand to get broken there - and that was just the beginning of her collapse.
Trailing 6-5, and serving at love-40, Vinci missed her first serve, then was called for a foot fault on a second serve. That resulted in a double-fault, ceding the set.
As she walked to the sideline, Vinci looked at the line judge who made the call and smiled sarcastically, giving him a thumb's up and applauding with her racket.
''If they called it,'' Vinci said later, ''I must have done it.''
It's a rare ruling in Grand Slam tennis, especially at a critical juncture, although there was, of course, the most famous foot fault of all on the very same court.
In the 2009 U.S. Open semifinals, Williams was angered by the same type of call: a foot fault that resulted in a double-fault; in that instance, it set up match point for her opponent, Kim Clijsters. Williams brandished her racket and yelled at the line judge, and the point she was docked for that ended the match.
This time, the call ended the competitive portion of Vinci's quarterfinal: She managed to take only 10 of 38 points the rest of the way.
Vinci has been dealing with an injured left Achilles tendon - she wore black tape in the shape of a ''V'' that framed her left calf - and a bad back. Still, her varied game, filled with slices and drop shots and net rushes, gave Kerber fits for most of the first set.
''I was playing better than her,'' said the 33-year-old Vinci, who mentioned at her news conference that she will decide after the season whether to retire.
But Kerber hung in there to reach her first U.S. Open semifinal since 2011.
''I'm staying more positive and believing in my game,'' Kerber said. ''I think that right now, I can win matches like that.''
Follow Howard Fendrich on Twitter at http://twitter.com/HowardFendrich