World number two Roger Federer won his second game of the day on Friday as he beat Stan Wawrinka to reach the semi-finals of the Cincinnati Masters.
The seven-time champion, who began his day with victory over Leo Mayer, beat fellow Swiss Wawrinka 6-7 (2-7) 7-6 (8-6) 6-2.
The match was interrupted for 21 minutes as the players and crowd left the court during a lightning storm.
"It's quite unusual to stop for lightning," Federer said.
"I didn't know if it meant the end of the night or that we would come back. But I got my energy back for the third set, a momentum shift was good for me.