For the second consecutive year, Serena Williams bowed out in the semifinals of the US Open.

Two matches in less than 24 hours proved to be too much for Williams, who fell to 10th-seeded Karolina Pliskova 2-6, 6-7 (5).

Coming back to the court after a tough three-set quarterfinal against Simona Halep the night before, Williams looked physically and mentally drained Thursday night. She also appeared to be struggling with a left leg injury that severely inhibited her movement.

Unlike Roberta Vinci, who bested Williams in 2015, this time Williams was outdueled by a fellow heavy hitter. Like Williams has done to so many opponents before, Pliskova overpowered her on serve and Williams struggled to react.

The 24-year-old Pliskova, who had never before made it past the third round of a major, becomes the first person to best both Williams sisters at the same Slam since Kim Clijsters did so in 2009.

Williams was looking to break Steffi Graf’s Open era records for most Grand Slam wins and consecutive weeks at number one. Instead, Williams will stay at 22 Grand Slams and her reign atop the WTA will end at 187 consecutive weeks.