The DPi entries from Cadillac and Acura were evenly matched as the Daytona 24 Hours reached 25% distance.
Mike Conway held sway at the front of the field on six hours, with the #31 Action Express driver leading by seven seconds from Helio Castroneves in the best of the Acura ARX-05s.
Conway moved into the ascendancy late in the sixth hour when he overtook both Castroneves and long-time race leader Christian Fittipaldi during the tail end of a heavy rain shower.
The #31 Cadillac had already recovered from a drive-through penalty for team-mate Stuart Middleton, who tagged the second Penske-Acura car into a spin at the horseshoe hairpin three hours in.
Up to Conway taking the lead, the sister #5 Action Express Cadillac of Fittipaldi, Joao Barbosa and Filipe Albuquerque had commanded most of the IMSA Sportscar Championship season opener.
Albuquerque took to the front at the opening round of pit stops, before he and his team-mates opened up a comfortable advantage over the rest of the prototype field.
The AXR crew's lead was cut back by the race's only full course caution period in the third hour, when the Performance Tech ORECA stopped on-track in the speedway, but Barbosa soaked up the pressure at the restart and drew out the advantage again.
It wasn't until the sixth-hour wet weather spell that a new permanent leader emerged, as Castroneves first overtook Fittipaldi before Conway surged past both.
The Wayne Taylor Racing Cadillac dropped out of the top five when Jordan Taylor picked up a right-rear puncture in hour five, but has since recovered to fourth, while Dane Cameron positioned the second Penske-Acura DPi in fifth after six hours.
Two-time F1 champion Fernando Alonso briefly led the race overall on his endurance debut behind the wheel of the United Autosports Ligier LMP2, which sat sixth at the chronological milestone.
The Spaniard's time at the front came during a pit cycle at the end of a stable opening stint, while an impressive run from Norris just after the rain period elevated the #23 Ligier-Gibson into a competitive position.
Norris worked his way from sixth up to third as the track began to dry, and assumed the lead when when Castroneves and Fittipaldi pitted. The 18-year-old then surrendered his advantage to Conway by pitting shortly before the first six hours were up.
There have been no retirements in the top category thus far, although both Joest-Mazda DPis have struggled with various issues including a recurring gearbox problem for the #77 and punctures for the #55.
The pair of Nissan DPis showed well early on, with Nicolas Lapierre setting the fastest lap in the #22 car and Pipo Derani moving up to second for a period, but both Ligier-based cars lost ground with separate puncture episodes.
In GTLM, Ford dominated the opening six hours through its #66 car co-driven by Joey Hand, Sebastien Bourdais and Dirk Mueller.
Bourdais was eight seconds ahead of Scott Dixon in the sister Ganassi car, with the Risi Competizione Ferrari 488 a further five seconds adrift in third.
The opening stages were controlled by Hand, who overtook pole-sitter Jan Magnussen's Corvette at the start before settling into a one-two with the #67.
The tailgunner car then dropped places through a slow opening pit stop, leaving the #66 alone out front, but it gradually recovered as the Fords exhibited the best pace during the tentative early running.
During the rain period, Porsche's Patrick Pilet opted to stay out on slick tyres to close in on the Fords, which had both switched to the wet compound.
That move appeared to pay dividends as Pilet started to shape up a challenge on the top three when the six-hour mark came to pass.
The Land Motorsport Audi squad led GTD at 25% race distance, with Kelvin van der Linde holding station ahead of Jeroen Bleekemolen (Mercedes) and Mario Farnbacher (Acura).
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