After 20 years in professional tennis, Andre Agassi has faced more big serves than he might care to remember. Years ago, he faced bullets from Marc Rosset, a 6-foot-7 Swiss slugger who squared off against the game’s greatest returner six times. More recently there was Joachim Johansson, the talented Swede who served 51 aces against Agassi at the Australia Open this year – and lost. And who could forget Goran Ivanisevic, the bridesmaid of Agassi’s lone Wimbledon title, or that guy by the name of Sampras?

As tall as those serves were, Agassi said Ivo Karlovic’s might stand above of them all. Karlovic, the 6-foot-10 Croatian with stilts for legs and a lethal right arm, played Agassi for the first time yesterday, and he proved a mighty test.

In a peculiar and awkward match that lasted two hours and 30 minutes, Agassi needed all the patience and concentration he could muster before he prevailed in three tiebreaks, 7-6 (4), 7-6 (5), 7-6 (4). Rallies were rare, games were short, and Karlovic finished the afternoon with 30 aces, two fewer than he hit in his first-round victory over American Mardy Fish. Agassi managed a break of serve in the second set, but he squandered a 4-1 lead.

“It’s an incredible serve,” Agassi said. “The trajectory is the main issue, because you’re lunging, but then it’s up [high]. You’re sort of diving, but then you can’t reach it, even if you dive perfectly and on cue.”

Agassi tried lunging, he tried stepping forward, he tried standing farther back. Many times, he picked a spot and just hoped that he had guessed correctly. If he did, and the two started a rally, Agassi won by consistency alone, exposing Karlovic’s wild strokes and waiting for him to lumber toward the net – prime position for an Agassi passing shot. In the first set, Agassi won 29 of 41 points once either his or Karlovic’s serve was returned into play. Put simply, once the two played tennis, Agassi won nearly three points to Karlovic’s one.

“If I was coaching him I’d fine him a hundred dollars every time he hit a ground stroke,” Agassi said. “I would. He’d play like Paul Annacone – stick your racket out and come forward.”

Though Karlovic did not quite follow the strategy Agassi advised, he still came within a point of winning the first set when Agassi served at 5-6.Agassi closed the opening with a forehand crosscourt passing shot and then took the tiebreak despite falling behind 2-0.

“Today required a lot of concentration because it only took a mental lapse for one or two shots and the set’s over with,” Agassi said. “It’s really difficult mentally to stay the course.”

Several tests remain before Agassi, twice the champion here, reaches a potential quarterfinal match against Rafael Nadal next Wednesday. Tomorrow he will face a young Czech, Tomas Berdych, seeded no. 32, and then on Monday perhaps Russian Mikhail Youzhny, seeded no. 24.

While Agassi will undoubtedly impose his will on court, the intangibles he cannot control – good weather and good health – are so far going his way. He said his back, troubled lately by an inflamed sciatic nerve, has responded well to a recent cortisone shot.

“It was a good sign to play a guy where I had to lunge a lot and jump around,” he said. “I felt pretty good.”

As for Karlovic, he took solace in pushing a legend to his limits over three sets. If he can improve his strokes, Karlovic said, he will be a dangerous player next year. And if not, there’s always time for a second career.

“If you know any NBA agents, let me know,” he said. “I can play pretty good.”