Rotterdam: The seeds in action at the Rotterdam World Tennis on Thursday suffered differing fortunes, with two going through and two going out.
Holder and top seed Juan Martin del Potro moved safely through with a victory over unseeded Frenchman Paul-Henri Mathieu 6-2, 7-6 (7/2) in 86 minutes, which included 10 aces.
Czech third seed Tomas Berdych posted another near-perfect showing, also firing 10 aces and saving all four break points he faced against France`s Nicolas Mahut, inning 6-4, 6-3 to keep a perfect record on serve so far this week at the Ahoy stadium.
Del Potro will line up on Friday in the quarter-final against Latvian Ernests Gulbis, who upset eighth seed Grigor Dimitrov 6-4, 7-6 (7-3).
Pole Jerzy Janowicz, a winner over German sixth seed Tommy Haas 6-4, 6-4, will take on Berdych, an Australian Open semi-finalist.
Del Potro remained optimistic on the state of the left wrist which has bothered him for more than a month but which he says is on the mend under strict medical supervision from specialists in Minnesota.
Overall, the Argentine ranked fourth in the world, was pleased with another winning effort.
"It was another tough match, I had a letdown in the second set but at the end I was very solid, All that matters is that I got the win.
"My wrist is feeling better every day and I`m happy with the progress."
Berdych won his fifth match without dropping serve against Mahut, taking just 72 minutes. The Czech is playing the event for the eighth time and has a best showing of a 2012 semi-final but has also exited three times in the first round.
The player who finished in the ranking top 10 for the fourth year in a row, and stands seventh on the ATP, went through all of 2013 without a title after winning his last in autumn 2012.
He was the only top 10 player last season not to lift a trophy.
The Czech left the court smiling after his win lifted him into the Rotterdam last eight.
"I felt good on the court and I was hitting the ball very cleanly. I credit this win to my serve, which really helped me out. For me, serving was the key to the match."
Second-seeded wild card Andy Murray will aim to make it a top three sweep into the quarters when he faces Austrian qualifier Dominic Thiem later.
Thiem, aged 20, is the youngest player ranked inside the top 125 and will be bidding to reach his third ATP quarter-final after Kitzbuhel and Vienna last season.