Lleyton Hewitt had a comfortable win in his first match since the Australian Open, beating American Paul Goldstein 6-4 6-2 at the SAP Open in San Jose.
Hewitt lost in the second round of the Australian Open
"I'm not quite 100%, so it's nice to get through," said Hewitt, who has been struggling with an ankle injury.
"I felt like I moved a lot better in the past. It's a bit of confidence with pushing off the ankle."
Britain's Andy Murray faces Taiwan's Yeu-Tzuoo Wang in the early hours of Friday, UK time, in the second round.
On a good day for Australia, former San Jose champion Philippoussis had his first win over a top-15 ranked player for more than two years.
Philippoussis beat fourth seed Tommy Robredo 3-6 7-5 7-5, and said: "This win is a result of all the hard work I've been putting in.
"If I stay patient and keep working, I know the results will come."
Meanwhile, John McEnroe returned to ATP action with a doubles win. He and Jonas Bjorkman beat Wayne Arthurs and Stephen Huss 6-3 6-3.
McEnroe, who turns 47 on Thursday, was playing an ATP Tour match for the first time since 1994.
"I want to inspire the old people," McEnroe said. "The old dog wants to teach the young guys a few new tricks."