'Phenomenal' Fernando Alonso can claim to be F1's best - Mario Andretti

Mario Andretti thinks Fernando Alonso's "phenomenal" debut at the Indy 500 has raised his stock in Formula One enough that he can claim to be the sport's best driver.

Alonso enjoyed a stellar drive at his rookie appearance at an oval, remaining a contender for much of the race until a late Honda engine failure forced him to retire. The Spaniard has not won an F1 race since May 2013 and since 2015 has been hindered by a succession of uncompetitive and unreliable Honda engines at McLaren.

Andretti, a former world champion and the winner of the 1969 Indy 500, believes Alonso showed his talent by adapting to oval racing so quickly.

"Phenomenal," Andretti told ESPN on how he rated Alonso's performance. "I'm so, so impressed, and not surprised one bit because he showed that poise from the very beginning at practice. He was out there maximising at all times possible, trying to test in all possible conditions.

"In the race I thought a lot of things would be thrown at him -- you know what, they did and he knew what to do with it. I'm totally impressed and that's what I feel so sorry for him to be let down on what should have been a really happy day. He would have had an interesting end to this race."

When asked if he felt Alonso can now go back to F1 and claim he is the most complete driver on the grid, Andretti nodded and said: "I guarantee that his stock is raised, no question about it. That respect, he deserves it. He did everything he needed to do, plus. So you can't beat that. There were no losers here. Except for that one engine!"

Alonso will return to the Formula One paddock for the Canadian Grand Prix in Montreal and faces the prospect of a frustrating few months until the summer break. It is after that point Alonso has promised he will make a decision on whether to stay at McLaren or look elsewhere for 2018 -- though his chances of finding a title-winning car look slim.

Andretti, who suggested ahead of the Indy 500 Alonso should consider a full season in IndyCar next year, thinks the Spaniard's fortunes will improve before this season has concluded.

"It is difficult. The only thing that keeps a driver happy is to be competitive, anything else is total frustration and you don't know who to take it out on! I feel sorry for him, he's at the top of his game and wasting time. McLaren is feeling the same pain obviously because that's a team that only knows how to be in front and they are paying the cost with him -- that's why they backed him on this effort to try and get a smile on his face. He had it until the end of the race!

"It can only get better for him from here in terms of Formula One, it looks like they have a chassis for sure. The engine situation, it's going to get better. I'm sure he's going to be in the points before the season is out."

Alonso's performance earned him the Indy 500 Rookie of the Year award.