Second seed Nikolay Davydenko easily came through a potentially tricky first-round match against Feliciano Lopez at the ABN Amro World Tennis Tournament in Rotterdam, while Andy Roddick also found the going easy in San Jose.
Davydenko cast aside last week's SA Tennis Open champion 6-4 6-2 in 75 minutes.
Unseeded Lopez claimed his first ATP Tour title in more than five years in Johannesburg last week but was no match for the Russian, who was playing his first match since losing to eventual champion Roger Federer in the quarter-finals of the Australian Open last month.
Fourth seed Gael Monfils battled back to defeat Belgian Olivier Rochus 4-6 6-1 6-2.
Monfils has been feeling unwell but, after conceding the opening set, he reeled off 12 of the next 15 games on the back of 19 aces.
The Frenchman will next meet local hope Thiemo de Bakker.
World No.8 Robin Soderling booked his place in the last eight with a 7-6 (8-6) 6-2 win over Dutch wildcard Igor Sijsling.
The 25-year-old is playing his first tournament since the Australian Open, where he struggled with elbow tendinitis as he made a first-round exit.
A right arm injury forced Viktor Troicki to retire from his match with Jurgen Melzer, with the Serbian trailing 6-3 3-0.
Michael Berrer also progressed after an epic first-set tie-break to beat Arnaud Clement 7-6 (18-16) 4-6 6-4.
Andy Roddick was untroubled as he opened his SAP Open bid for a fourth title in San Jose.
The American, the winner of the tournament in 2004, 2005 and 2008, claimed a 6-1 7-6 (7-1) victory over qualifier Ryler Deheart as he began his bid to reclaim the title in his ninth appearance.
Roddick, who was playing in his first match since the Australian Open, will now meet Leonardo Mayer of Argentina in the second round.
Radek Stepanek, who was looking to reach his third final in three appearances and lost to Roddick in 2008, was eliminated in the first round.
The third seed from the Czech Republic was beaten 6-3 6-4 by Xavier Malisse of Belgium, who will now meet Michael Russell in the second round.
In the day's other first-round contest, Fernando Verdasco of Spain prevailed 6-3 6-7 (8-10) 6-3 against Lu Yen-hsun of Chinese Taipei and will next meet Germany's Benjamin Becker.
There were three second-round contests, with fourth seed Tommy Haas joining Stepanek in falling out of the tournament.
Haas was beaten 7-6 (7-3) 6-2 by Denis Istomin of Uzbekistan.
Istomin will meet Philipp Kohlschreiber in the quarter-finals after the sixth-seeded German defeated Dudi Sela 6-2 6-0.
Fifth seed Tomas Berdych beat Jarkko Nieminen of Finland 6-3 6-2.
Berdych will meet Roddick or Mayer in the last eight.
Top seed Juan Carlos Ferrero defeated Nicolas Massu in three sets to progress to the quarter-final of the Brasil Open in Costa do Sauipe.
The former world No.1 beat his Chilean rival 6-2 5-7 6-2 in two hours 24 minutes in the second round match at the clay court tournament.
Spain's Ferrero will meet qualifier Carlos Berlocq in the last eight after the Argentinian defeated his compatriot Juan Ignacio Chela 7-6 (7-5) 6-2.
Fourth seed Igor Andreev and sixth seed Pablo Cuevas also progressed and will meet each other for a place in the semi-finals.
Russia's Andreev defeated qualifier Rui Machado of Portugal 6-3 5-7 6-4, while Uruguay's Cuevas defeated another Portuguese player, Frederico Gil 7-5 4-6 7-6 (7-3).