The world number one Novak Djokovic had to save four set points as he endured a lengthy first set tie break, in beating Ukrainian Alexandr Dolgopolov to reach the US Tennis Open quarter-finals.
Djokovic won in straight sets against Ukranian Alexandr but only after winning the first-set tiebreaker 16-14.
Roger Federer was left waiting until almost midnight in New York to begin his fourth round match but made up for the delay with a brutal 6-1 6-2 6-0 win over Juan Monaco of Argentina to reach the quarter-finals.
The women's world number one Caroline Wozniacki was two games away from being eliminated by former champion Svetlana Kuznetsova before winnings 6-7, 7-5, 6-1 to reach the quarter-finals.
Three-time champion Serena Williams is also through to the final eight.
