It was a joyous, impromptu family reunion in the Andretti Green Racing pit box after the Menards Infiniti Pro Series Grand Prix of St. Petersburg.

The party quickly grew to include extended family - Andretti Green Racing drivers, team co-owners and crew members - and carried over late into the afternoon as everyone feted the man of the hour.

Marco Andretti won the 40-lap race on the 1.8-mile, 14-turn course along Tampa Bay in his series debut. Not bad for a high school senior.

Mario Andretti greeted his grandson - before he climbed from the No. 26 Vonage Dallara/Infiniti/Firestone - with a bear hug. The 1969 Indianapolis 500 winner said he was "on pins and needles" as he watched the first non-oval race in series history.

"He drove so hard, drove his heart out. It was awesome," he said, a smile crossing his tanned face.

Michael Andretti, who has tasted his share of glory and heartache in a long competitive driving career, was obviously a proud father. He also clamped his arms around Marco before he could put a foot on the ground.

"He drove like a champion already," said Andretti, co-owner of Andretti Green Racing who said it's likely additional Menards Infiniti Pro Series races will augment Marco's Star Mazda series scheduled events. "I'm impressed."

Marco sheepishly accepted congratulations from family, friends and general well-wishers after claiming the 1.4181-second victory over Wade Cunningham. But the mood was tinged with sadness. William Riehl, 18, a close friend of Marco Andretti, was killed in an automobile accident April 2. He was scheduled to travel to St. Petersburg to spend the rest of the weekend with Andretti family.

"I think once I get the helmet on, it helps me get away from it," he said. "I did what he would want me to do. This is for him."

Andretti is the youngest driver to win a Menards Infiniti Pro Series race and joined A.J. Foyt IV, Mark Taylor and Phil Giebler as winners in their inaugural event. But he drove like a veteran the entire weekend.

"Every race I go into, I don't expect to win, but I know I have a chance," said Andretti, who won the pole position on April 2. "After I made the mistake (getting hung up in Turn 10 on Lap 13, allowing Cunningham to pass him), I knew I wasn't done. I just felt I was going to come back. No more mistakes. That was the mistake for the race, and now put your head down, and we got lucky with lapped traffic."

Andretti remained close to Cunningham over the next 16 laps. After both approached lapped traffic in Turn 3, Andretti slipped past.

"I was trying to slow down the race and conserve my brakes (while in the lead)," said Cunningham, who has started his rookie season with fourth-, third- and second-place finishes in the No. 33 Visit New Zealand entry for Brian Stewart Racing. "I ran into a little brake trouble, and I couldn't do any heavy braking, so when (Marco Andretti) got the lead there was no way I could stay with him though the heavy braking zones to make a pass.

"It's a long championship. I'm sitting pretty good now (second in points). I'm pretty disappointed but I was looking at the long picture at the time."

Nick Bussell finished third in the No. 21 JL West Motorsports entry.

"The last couple of laps I used everything I had, he said. "This venue is nice. The street course is awesome. The fans were great and I had a good time with them last night at the autograph session."

He was followed by two drivers with a heritage of auto racing greatness. Al Unser, who started seventh in the No. 3 Brian Stewart Racing entry, was fourth, and Arie Luyendyk Jr. moved from an eight-place starting position to fifth.