Two-time Indy 500 champion Takuma Sato posted the fastest lap at Indianapolis Motor Speedway in 27 years on Friday to pace the last practice before qualifying.

Defending champion Marcus Ericsson was close behind him, making Chip Ganassi Racing the team to beat heading into qualifying weekend for "The Greatest Spectacle in Racing."

Sato turned a lap of 234.753 mph early in the six-hour practice, the fastest since 1996, before posting a four-lap average of 233.413 with about 16 minutes to go and rain bearing down on the speedway.

Sato admitted afterwards he was "on edge" as he coaxed as much speed out of his Honda as possible.

"I think we're very satisfied with our performance," he said.

So was Ericsson, who is in a contract stalemate with Ganassi, and along with Sato knocked Team Penske's Josef Newgarden and Australian Will Power down a notch.

Ericsson had the second-best four-lap average of 233.113 mph on a rapidly cooling track.

"Earlier today I was struggling a bit. The car was fast but I couldn't do four laps," Ericsson said. "To come out and get a solid run - a solid four laps, still a little too much drop-off - but happy with that and right up here again."

Sato was fastest in Wednesday's practice and Ericsson was quickest Thursday. Both of those days, Ganassi teammate Scott Dixon was right behind, but he said a problem during his qualifying simulation Friday forced him to shut down early.

"We'll just have to see," said Dixon, the 2008 Indy 500 champion. "It'll definitely put us on the back foot a bit."

Newgarden, who was fastest during the April open test, felt optimistic after posting the third-fastest four-lap average late in the practice.

That positive attitude took a hit when he drew the 34th - and least favourable - qualifying slot about an hour later.

Pato O'Ward had the fastest trap speed at 243.142 mph as teams enjoyed the extra boost they will use for qualifying.

"I wasn't aware of what we hit in the trap speeds until I saw it. It was frickin' fast," said O'Ward, who was second to Ericsson in last year's race.

"The engine sound was beefier and it sounds frickin' fast, and it feels fast. It's cool."