NEW YORK (Reuters) - Serena Williams fought back from a break down in the first set to beat Czech eighth seed Karolina Pliskova 6-4 6-3 and reach the semi-finals of the U.S. Open in suffocating conditions on Tuesday.
The 36-year-old, who is bidding for a record seventh title at Flushing Meadows as well her 24th career Grand Slam crown, started sluggishly at the Arthur Ashe Stadium , allowing Pliskova to take a 3-1 lead in the opening set.
With the heat rule in effect and junior matches on the outside courts suspended earlier in the day, Williams made 22 unforced errors in the opening set but showed all of her big-match pedigree to battle back and close out the set by winning the last four games.
"The crowd was really rooting for me and I felt so bad because everyone out here was cheering and I wasn't winning so I thought I had to try harder," Williams said courtside.
"I really feel like right now I'm playing free. I was having a baby this time last year so I have nothing to prove."
The second set was far more comfortable for the number 17 seed.
Two successive breaks of serve allowed Williams to win her eighth game in a row and open up a 4-0 lead, and she saw off a brief fightback from Pliskova before sending down her 13th ace to seal the match in one hour and 26 minutes.
"When I get to a Grand Slam, I feel I want to play really hard. I want to do really well. I love this game so maybe that's why," added Williams, who was beaten by Pliskova in the 2016 semi-finals.
Next up for the American is a semi-final clash with 19th seed Anastasija Sevastova of Latvia.
(Reporting by Simon Jennings; Editing by Peter Rutherford)