The reigning IndyCar Rookie of the Year hadn't finished better than second in 39 IndyCar and Champ Car races.
"I've been working for this my whole career," Pagenaud said. "It's freaking awesome."
Mike Conway, who won Saturday's race with just three cautions, finished third.
Scott Dixon was fourth, followed by Dario Franchitti and Marco Andretti, who pulled into a tie with Helio Castroneves for the IndyCar points lead.
U.S. women shut out Canada
Soccer • Alex Morgan scored twice and Sydney Leroux added a goal to lead the United States over Canada 3-0 in Toronto in their first meeting since the Americans' 4-3 overtime win in the semifinals of last year's Olympic women's soccer tournament.
Morgan scored for the top-ranked Americans in the 70th minute when she cut inside defender Emily Zurrer and from the top of the penalty area slotted past goalkeeper Erin McLeod.
Morgan scored from the same spot two minutes later, her 44th international goal.
Veilleux wins first stage by 2 minutes
Cycling • David Veilleux of Canada won the first stage of the Dauphine Libere race by nearly two minutes. Gianni Meersman of Belgium was the runner-up, finishing just ahead of the main pack in Champery, Switzerland.
Veilleux won the 75-mile ride in 3 hours, 17 minutes, 35 seconds. Meersman was 1:56 back.
From wire reports