Detroit IndyCar: Andretti's Carlos Munoz takes shock win in wet

Changing conditions had the entire field trying to second-guess the weather right from the start, and on speed alone, Munoz might not have been a contender.

The key move came when he, team-mate Marco Andretti and Penske's Simon Pagenaud stayed out on slicks after everyone else had changed to wets in anticipation of more rain.

Andretti was leading at that point, and he and Pagenaud stopped together on lap 40; four laps later than previous leader Will Power, and at a time when the slicks were still almost 20 seconds per lap faster.

Munoz, however, stayed out longer still. When the Colombian rejoined after making his own switch to wets three laps later, he returned to the track with a lead of almost 20s over his team-mate.

Over the next seven laps he extended that gap to 30s, but at that point the arrival of lightning in the area forced the series to throw a red flag with 23 laps remaining.

Later, with conditions failing to improve and light beginning to fade, the decision was made not to restart the race.

Munoz's victory was the first for Honda since James Hinchcliffe's win at NOLA - also in the wet - and Andretti held on to second for a team one-two, with Pagenaud completing the podium.

The tricky conditions bred a total of eight caution periods, mostly for debris or to retrieve cars from the barrier after contact.

Most incidents were relatively minor, and the one exception came on the first restart when Stefano Coletti brushed James Jakes, who wobbled into Tony Kanaan, who in turn was pitched into the outside wall and squarely into the path of Graham Rahal.

All but Rahal were able to continue, although Kanaan lost a lot of time in the pits undergoing repairs.

The only other accident-related retiree was Charlie Kimball, who lost control all by himself shortly after switching to slicks and clattered hard into the outside barrier at Turn 2.

RESULTS - 48 LAPS: