The pressure of Serena Williams' pursuit of Grand Slam history caused her to choke in the Australian Open quarterfinals, says John McEnroe.

Williams led Karolina Pliskova 5-1 in the final set and squandered four match points as the Czech won six straight games shocking a hobbled and shaky Serena, 6-4, 4-6, 7-5, to charge into her first career Australian Open semifinal. Williams rolled her left ankle while holding a 5-1 third-set lead and never won another point on serve.

Serena: I Didn't Choke

Pliskova's comeback denied Williams' quest to claim her 24th Grand Slam singles title and equal Margaret Court's all-time record.

Former world No. 1 McEnroe says the pressure got to the 37-year-old American.

"As you get older, you realize you have less opportunity maybe to pull this off," McEnroe told Australia's Nine Network. "So you put more pressure on yourself. It looked like at the end, the pressure, which is very rare—I didn’t think I would be saying this—but the pressure of the moment got to her a bit.

"(It is) a little bit of choking, yeah. Let’s face it, they’re all human beings."

The seven-time Australian Open champion said she didn't choke on match points moments, crediting Pliskova for playing her best under pressure.

"I don’t really take losses well, but like I said, Karolina literally played lights out from 5-1, like literally I’ve never seen anything like that," Serena said afterward. "There’s nothing I did wrong on those match points. I didn't do anything wrong. I just stayed aggressive. She just literally hit the lines on some of those points.

"One she hit an ace, unreturnable serve. Like I literally did everything I could on those match points. It's not like, I can't say that I choked on those match points. She literally played her best tennis ever on those shots. I can't really say that it's incredibly painful as opposed to what can I do better, you know, yeah."

Williams' coach, ESPN analyst Patrick Mouratoglou, said on ESPN he doubted Serena would have been healthy enough to play the semifinal had she closed the lead vs. Pliskova because of her ankle injury.

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