Dusan Lajovic breezed past James Ward 6-1, 6-3, 6-2 to bring Serbia level 1-1 with title holder Britain in their Davis Cup quarterfinal.
The second singles could not be played on the opening day because of rain and was postponed until Saturday, when it also began an hour later than scheduled.
But the weather then held up and Lajovic put Serbia back in the match. He won 10 straight points in breaking Ward at love and holding at love for a decisive 3-1 lead in the third set.
The doubles were being played later Saturday.
Britain took a 1-0 lead when Kyle Edmund beat Janko Tipsarevic 6-3, 6-4, 6-0 in the opening singles.
Serbia is without top-ranked Novak Djokovic, while Britain is missing No. 2 Andy Murray, the Wimbledon champion.
Murray, however, came to Belgrade to support the team from the sidelines, while Djokovic stayed away.
Lajovic broke serve in the opening game and that set the tone for the match.
"A tough start, he didn't do much wrong," Ward said. "It's one of the heaviest clay courts I've ever played on, it doesn't suit my game at all."
"It's not my ideal surface in slow and heavy conditions. He was just too good today," Ward said.
Lajovic agreed about the condition of the clay court after heavy rains overnight.
"As soon as you put pressure on your foot, it falls apart," Lajovic said.
"I was a a little under pressure as we were down 1-0, but I think he was a little less comfortable. I played a good tactical match."