Alexander Zverev, the world No 3, has moved smoothly into the quarter-finals of the Vienna Open.
The German needed only 72 minutes to defeat American Marcos Giron 6-2 7-5 on Wednesday. He will now face either Italy's Lorenzo Musetti or France's Gael Monfils.
"He served incredibly well in the second set, so I'm very happy that I managed it in two sets," Zverev said.
The Tokyo 2020 Olympic champion is still suffering the consequences of pneumonia, which forced him to miss the China Open in Beijing last month.
"I'm not completely fit. It takes months, but I'm feeling better and better," he said.
Meanwhile defending champion Novak Djokovic has withdrawn from next week's Paris Masters.
Djokovic, 37, played at the Six Kings Slam exhibition last week but organisers did not give a reason for his withdrawal.
Djokovic has won a record seven titles at the Paris indoor tournament. His decision not to play could jeopardise his chances to qualify for the year-end ATP Finals.