SEATTLE -- The San Antonio Spurs will be without their starting center, David Robinson, again Saturday when they face the Seattle SuperSonics in Game 3 of their first-round playoff series.

The series is tied at 1, with Game 4 to be played here Wednesday night. Robinson, who did not travel to Seattle, is doubtful for that game, Spurs coach Gregg Popovich said on Friday.

Robinson's sprained lower back kept him out of Monday night's game in San Antonio, when the Sonics evened the series with a 98-90 victory. He played only seven minutes in Game 1, a 110-89 Spurs' win.

The underdog Sonics, the No. 7 team in the West, believe they can beat the Midwest Division champion Spurs, and they think they have a much better chance to do it with Robinson out. The 7-foot-1 center, a 10-time All-Star, averaged 12.2 points and 8.3 rebounds during the regular season.

"Two big towers like that in the middle is a lot different," Sonics All-Star point guard Gary Payton said. "You know if you get away from one, the other one is going to be there."

With Robinson missing, 7-foot power forward Tim Duncan had to play 47 minutes in Game 2. He had 32 points and 12 rebounds, but shot 9-for-19, a sure sign of a fatigued player.

The Sonics outrebounded San Antonio 49-35, with Payton leading his team with 11 rebounds and Vin Baker collecting 10.

Robinson's absence hurts the Spurs' rebounding as well as their defense, Seattle coach Nate McMillan said.

"You're missing a 7-footer," he said. "It does limit what they can do as far as their defensive schemes. Without David, they lose that size when they double team and trap the ball on the weak side trying to rebound."

Duncan, a top MVP candidate this season after averaging 25.5 points and 12.7 rebounds per game, hopes Robinson can get back for at least some of the Sonics series.

"It's a lot tougher doing it without him," he said. "We really missed him in situations like the last game. We have to do better as a team, keeping our blocks out and putting bodies on people."

San Antonio forward Malik Rose was confident the Spurs could overcome the loss of Robinson.

"We're the Spurs," he said. "It doesn't make a difference. David is a huge, huge loss, but we know what we are capable of doing."

Popovich said he wouldn't change his approach significantly.

"We're too late in the season to change a whole lot," he said. "Not having David obviously changes the things we do, but we have to make those adjustments. In the end, nobody cares who's here or healthy. They care who wins and loses."

Popovich said Robinson's injury does not appear to be career threatening.

The Sonics could be missing a key player, too. Vladimir Radmanovic, an athletic 6-10 rookie forward, has a sore big toe in his right foot that kept him out of practice this week. He was listed as questionable for Saturday's game.

He hasn't been 100 percent since spraining his toe. He was on the injured list from March 22 to April 5 with his toe injury.

In Game 2, Radmanovic played 22 minutes, scoring five points and getting five rebounds.

The Sonics wouldn't have gotten a playoff split in Texas without the improved play of Baker. The four-time former All-Star power forward fouled out against Duncan in game 2, but he scored 15 points to go with his 10 rebounds.

He thinks the Sonics have a good chance to beat the Spurs twice in Seattle, because they'll be playing at home.

"I'm not taking anything away from the Alamodome, but I really think the Key Arena is a special place to play in the playoffs," Baker said. "I think our fans are going to give us a boost."

Seattle forward Rashard Lewis said the Sonics don't want to give the home-court advantage back to the Spurs. Game 5, if necessary, will be played in Texas next Friday.

"We definitely don't want to go back to San Antonio," Lewis said.

Both of Seattle's regular-season wins over San Antonio came at the Key Arena, but the Spurs are a good road team. They went 26-15 on the road this season and won their last four straight on the road. Their last road loss came March 31 in Los Angeles against the Lakers.

The Spurs planned to fly back to San Antonio after Saturday's game, return to Seattle on Tuesday and hold a shootaround Wednesday before Game 4.