NEW YORK -- It all started so well for Mark Philippoussis.

Hampered by knee trouble that has resulted in three surgeries over 14 months, the hard-hitting Australian came into the U.S. Open unseeded. He took the first two sets from No. 24 Sjeng Schalken on Tuesday and even after dropping the third, he seemed positioned for the upset.

Then, disaster.

Reaching for an overhead shot, he landed awkwardly and fell to the ground, grimacing as he grabbed his knee. Trainer Doug Spreen rushed to help and Philippoussis said, "I'm scared."

Spreen got him back on his feet and Philippoussis even won a game. But he was playing hurt and soon had to retire from the match won by Schalken 6-7 (7-1), 4-6, 6-3, 5-3.

"I think it's very tough for Mark," Schalken said. "It was very unfortunate. Hopefully he can play soon again."

Philippoussis left the National Tennis Center grounds.

"He was going to Miami to see the doctor who performed his last surgery in March, 2001," Philippoussis' agent, David Felgate, said. "He will have an MRI conducted tomorrow (Wednesday)."

Quitin' time

Through the first two days of the U.S. Open, a Grand Slam tournament-record seven men quit during first-round matches because of injuries.

That also ties the U.S. Open record men retiring over the course of an entire tournament.

The previous Grand Slam record was six in the first round at the 1998 U.S. Open. The high for an entire major tournament is eight, set at the 1998 Australian Open.

Happy birthday

Carlos Moya's 3-6, 6-4, 6-3, 7-6 (7-4) first-round victory over Adrian Voinea on Tuesday was a 26th birthday present for the Spaniard.

He's one of six men celebrating birthdays during the Open. The others are Juan Ignacio Chela (23) and Andy Roddick (20) on Friday, Tim Henman (28) and Greg Rusedski (29) on Sept. 6 and Sjeng Schalken (26) on Sept. 8.

Partners for success

Tracy Austin was honored for her role as a WTA Tour mentor on Tuesday night. Austin helped guide the career of Alexandra Stevenson.

"She's a great champion," said Stevenson, once a Wimbledon semifinalist. "I wish I could be like her some day. It's just great that the WTA assigned me Tracy. She's been a wonderful mentor. I know it's going to keep continuing even though I've graduated. She'll always be there for me."

The program assigns a senior player to a young player for guidance.

"I came up at 14 with my mom," Austin said. "We had no idea what we were doing. We had no idea which tournaments to enter, how many tournaments to play. There's a zillion and one questions that you would love to ask somebody that's already been there, somebody that you trust. So I think it's a terrific program."

SmashZone tests fans

Fans at the U.S. Open can test their skills at the USA Tennis SmashZone, which features 12,000 square feet of tennis activities, including seven stations testing hand-eye coordination, accuracy and speed.

Fans can measure strength of serve or play the role of sports broadcaster by calling the action from a past U.S. Open match.

Clinics and player appearances are also scheduled.

No rest for the weary

No time to sleep in. There's a Grand Slam tournament to be won.

About 12 hours after winning her first-round match at the U.S. Open, Serena Williams was out on a practice court Tuesday at 10 a.m. Her father, Richard, was a few steps away, watching intently as the 1999 Open champion worked on slice shots.

Williams is here with his daughters -- Serena is seeded No. 1, two-time defending champion Venus is seeded No. 2 -- after not having made the trip to Europe for the French Open or Wimbledon.

Fans arriving at the National Tennis Center early Tuesday gathered beside practice courts to catch glimpses of Serena, as well as fourth-seeded Lindsay Davenport and 10th-seeded Amelie Mauresmo.

Doubles action

Australian Open champions Daniel Nestor and Mark Knowles were seeded No. 1 Tuesday for the men's doubles tournament.

Nestor and Knowles, who lost in the finals at the French Open and Wimbledon, will be trying to become the third doubles team in the past 50 years to reach the finals of each Grand Slam tournament in a season.

Nestor, from Canada, and Knowles, from the Bahamas, will play Spaniards Juan Ignacio Carrasco and Alex Lopez Moron in the first round.