Daly led the way in the #23 Dreyer & Reinbold Racing entry, setting a flying lap of 225.394mph around the 2.5-mile superspeedway.
The 34-year-old will make his 13th appearance in the crown jewel race in May, looking to better a highest finish of sixth.
Daly’s lap came with just 10 minutes remaining on the day, knocking off Meyer Shank Racing’s Helio Castroneves’ temporary hold on the top spot with 225.200mph.
“Good to get back in the swing of things here,” Daly said.
“The team did a great job of preparing all winter for this day. It’s only day one for us, but it was obviously a good day.”
While fastest on the opening day, Daly was still quick to downplay the result.
“There are several cars that aren’t running their race cars yet,” Daly said.
“It’s just testing, we can’t overreact to test results. But honestly, every time we went out there, we did seem to be pretty quick, which is good.
“Our mission this month is one day at a time.”
Two-time Indy 500 winner Takuma Sato took third position for Rahal Letterman Lanigan Racing with a best lap of 224.800mph.
Sato slotted in ahead of veteran Kiwi Scott Dixon (Ganassi) at 224.564mph and Ed Carpenter Racing’s Alexander Rossi with a 224.367mph lap.
Team Penske’s Scott McLaughlin ended the day eighth fastest on 223.687mph, two places ahead of Andretti Global’s Aussie Will Power (223.151mph).
Katherine Legge, recently announced as the 33rd entrant for the 110th running of the race, was not able to hit the track due to mechanical issues.
Josef Newgarden (Team Penske) led the way in the morning session – which excluded rookies and refresher program veterans – with a 223.415mph lap.
Sato was second at 222.850mph ahead of Arrow McLaren’s Pato O’Ward in third with a 221.842mph lap.
The Open Test resumes on Thursday April 30 AEST where all drivers will again hit the circuit in two sessions.
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