Carlos Munoz after 2nd-place Indy finish: I don't know how Rossi won

Indianapolis 500 champion Alexander Rossi admitted he didn't know how he pulled off a victory Sunday, and those sentiments were seconded by the man who finished right behind him in Carlos Munoz.

Related: Rookie Alexander Rossi wins the Indianapolis 500​

"I don't know how my teammate did it without stopping," Munoz said, as quoted by NBC's Motor Sports Talk. The 24-year-old was forced to pit with four laps remaining to refuel, but Rossi - who didn't pit for the last 12 laps - remained on the track on his way to the finish line.

The American rookie then ran out of fuel shortly after taking the checkered flag.

"If I'm honest, I want to know what he did," Munoz continued. "I will look. I am second, why he's not stopping? He's supposed to stop. I have to look and see what he did. I don't know what he did."

Munoz rocketed to the lead with five laps remaining, when he and eventual third-place finisher Josef Newgarden both went through pit lane. It appeared it was Munoz's race to lose, making Rossi's remarkable finish that much more disappointing for him.

"I knew I had this won," Munoz admitted to ABC's Rick Debruhl, before adding: "My car was flying. I was so good emotionally, physically, mentally."

Munoz was also the runner-up in the first Indy 500 of his career in 2013. He finished fourth in 2014, and 20th last year.