Tim Henman made the perfect start to his season with a 6-1 6-2 win over France's Nicolas Mahut in Las Vegas.
Henman showed few effects from his lengthy lay-off against Mahut
The 32-year-old has not played since October because of injury and illness but eased through the round-robin tie.
Having saved two break points in game one, the Briton reeled off four straight games to secure the first set and broke twice to take the second.
"To play so consistently, to not drop serve having not played for so long, it was a bit surprising," he said.
Friday night, Saturday, I felt awful, I was feverish and not really enjoying my experience of Vegas
Defending champion and top seed James Blake crashed out however, losing 6-2 6-4 to 19-year-old Russian Evgeny Korolev.
"I didn't play well, it happens," said Blake. "I'm not going to make a ton of excuses.
"I never really felt that comfortable. My game didn't click at any point."
But Lleyton Hewitt and Marat Safin were victorious in their opening round-robin matches.
Hewitt defeated fellow former champion Vince Spadea 6-3 6-3 while Russian third seed Safin swept aside Austrian Stefan Koubek 7-5 6-2.
Henman recovered from a knee injury but then missed the ATP event in Rotterdam with flu before picking up another virus on his arrival in Las Vegas.
606 DEBATE: Your reaction to Henman's victory
"Friday night, Saturday, I felt awful, I was feverish and not really enjoying my experience of Vegas," he said.
"But by Sunday, I came out here and hit for half an hour, started to feel better and then today I felt good on the court.
"I am just excited to be out on the court. I still think a little bit cautiously having had the knee injury and been out for quite some time, but to be playing with no pain and moving better and better is the most important thing."
Henman, the seventh seed, stated before the match he welcomed the round-robin style format as he was guaranteed to play two matches to ease back to match fitness.
However, he showed few ill effects from his lengthy lay-off and Mahut, 25, had no answer to the Briton's power.
Aided by a first-serve percentage of 70 in the first set, Henman took control after breaking for the first time in game four.
And it was a similar story in the second as the seventh seed saw out the final four games to seal victory, although he had to save three break points to serve out for the match.
Henman will now face Spain's Feliciano Lopez in his second group match knowing that another victory will see him through to the quarter-finals.