Lleyton Hewitt and Marat Safin, two former world number ones, made light of strong winds to earn morale-boosting victories in their opening round-robin matches at the Las Vegas Open on Tuesday.

Second seed Hewitt, who missed last week's event in Rotterdam because of a hamstring tear, beat American Vince Spadea 6-3, 6-3. Safin, fresh after a week off, defeated Austrian Stefan Koubek 7-5, 6-2.

Top seed and defending champion James Blake, however, faces a battle to make the last eight after he was humbled 6-2, 6-4 by 19-year-old Russian Evgeny Korolev.

Two-times former champion Hewitt continued his domination over Spadea, making it seven wins out of seven against the American.

Spadea gave himself a glimmer of hope when he fought back from 3-0 in the second set to level at 3-3 but Hewitt broke for 5-3 and held on to clinch the match.

Victory over Swede Thomas Johansson in his second match will ensure the world number 21 advances to the quarter-finals.

"It's never easy in those conditions," the Australian said. "You just have to be consistent, get a lot of balls in the court and try not to self-destruct."

Third seed Safin came through a testing first set before beating 30-year-old Koubek for the third time in three meetings.

The world number 25 Russian did not face a single break point on his serve in the match and is in pole position to qualify for the last eight. He plays compatriot Igor Kunitsyn in his second match.

"At the beginning of the match it was pretty tough but at the end I started to play much better," he said.

"When the weather is normal, you can start to play your best tennis, when it's like this it's more mental than normal tennis."

Seventh seed Tim Henman, playing for the first time this year after injury and illness, crushed Nicolas Mahut of France 6-1, 6-2 in his first round-robin match.

The world number 37 Briton, who took a wildcard into the event having not played since late October, was in fine form, wrapping up victory in just over an hour.

"To really play as consistently as I did, to not drop serve and having not played competitively for so long, it was a little bit surprising, to be honest," Henman said.

Blake was in trouble from the moment he dropped his opening service game against Korolev, one of the most promising young players on the ATP Tour.

Korolev lost his opening match to Argentine Juan Martin del Potro but after cruising through the first set against Blake, he broke to lead 4-3 and held on to keep alive his chances of making the quarter-finals.

Blake will now have to beat del Potro on Thursday to stand a chance of progressing.