Marco Andretti has aced the field following the opening day of practice for the 100th running of the Indianapolis 500.

Andretti, sporting a silver tribute helmet to his famous grandfather Mario Andretti, clocked a best of 228.97mph (368.49km/h).

The Honda driver led home an Andretti Autosport sweep with four of the team’s five cars leading proceedings.

“I know how this month goes. It’s definitely a roller coaster, so we’re prepared for that, but it’s a good opening day,” Andretti said.

“I think our team in particular looks pretty stout because we looked at the weather and moved things forward on the test plan from later in the week.”

Carlos Munoz was second with a 228.94 (368.44) effort ahead of Ryan Hunter-Reay at 228.03 (366.97) while rookie Alex Rossi continues to impress with a 226.86 (365.09) best lap.

“It was an eye opening experience this morning and I think we had a pretty successful first day,” the leading rookie Rossi said.

“The biggest thing is the group running. On my own getting up to speed is not a problem. Running as a pack at the end is interesting.”

Chip Ganassi star Scott Dixon broke what would have been an Andretti whitewash at the top by finishing fifth fastest in 226.83 (365.04) to push Townsend Bell, making a now customary cameo for Andretti, to sixth.

Team Penske eased into proceedings with points leader Simon Pagenaud mired in 16th while team-mates Will Power, defending champion Juan Montoya and Helio Castroneves were ninth, 13th and 27th respectively.

Pirtek Team Murray youngster Matthew Brabham had a trouble-free day, passing his mandatory Rookie Orientation test before ending 25th in open practice.

The session ran smoothly until inside the final 20 minutes when the caution was flown for debris on the track before it went green for the final 11 minutes.

Drivers will be permitted to turn up turbo boost on Friday during Practice 5 ahead of qualifying weekend.

See below for Indy 500 Practice 1 results