World number one Rafa Nadal battled back to defeat Frenchman Julien Benneteau 5-7, 7-6, 6-2 at the Cincinnati Masters on Thursday and Britain's Andy Murray needed a final set tiebreak to beat Latvia's Ernests Gulbis.
Third seed Roger Federer, coming off a runner-up finish in Toronto last week, enjoyed a free pass into the quarter-finals after his opponent pulled out of their match with an injury.
Nadal, who struggled to find his rhythm against a confident Benneteau, lost the first set and was then forced to save match point in the second.
With his French opponent struggling physically in the final set, Nadal showed his excellent fitness and cruised to victory and booked his spot in the quarter-finals.
Next up for Nadal is Cypriot Marcos Baghdatis who pulled off an impressive victory over Czech Tomas Berdych.
Murray also looked far from his best in the opening set against an occasionally inspired but often erratic Gulbis.
But Murray fought back in the second with the Latvian missing out on break point in the third game and hurling his racket to the ground three times before it was disfigured.
Gulbis had another good chance to get control of the match when he had break point in the eighth game of the third set but skied a shot high into the air and Murray held to make it 4-4.
With both players looking tired in the early afternoon heat another decisive moment went against Gulbis when, at 3-1 down, he had a straightforward smash opportunity but was dazzled by the sun and could only tap the ball into the net.
Murray gathered himself and won 4-6, 6-3, 7-6, setting up a quarter-finals match with American Mardy Fish.
Federer, who could set up a repeat of last week's Toronto final with Murray, sauntered into the last eight despite not having played a single set of tennis.
Less than 24 hours after his previous opponent retired hurt while trailing 5-2 in the first set, Federer's third-round opponent Philipp Kohlschreiber of Germany pulled out with a shoulder injury.
Since the Swiss maestro also had a bye in the first round, he will be well rested when he faces either David Ferrer or Nikolay Davydenko for a place in the semi-finals.Serb Novak Djokovic dominated his first set over Argentine David Nalbandian, winning 6-1, but then looked a little short of breath as he laboured in the heat, winning the second on a tie-break.