Matt Campbell set the early running with a 1m35.941s in the Porsche Penske Motorsports 963, although Jack Aitken soon joined him, the Action Express Racing Cadillac V-LMDh producing a lap just 0.032s slower.
At this point 2016 IndyCar champion Simon Pagenaud in the Meyer Shank Racing Acura ARX-06 lay third, and with 32 minutes to go, he trimmed his deficit to top spot down to 0.182s.
Right from the word go, Yelloly turned some very encouraging times in the #25 BMW M Hybrid V8, getting down to a 1m36.452s – only 0.511s away from Campbell – but with 24 minutes to go in the session it was six-time IndyCar champion Scott Dixon who jumped to the top of the times in the #01 Chip Ganassi Racing-run Cadillac V-LMDh with a 1m35.717s.
That survived until with 16 minutes to go, Alexander Sims of AXR produced a great lap to eclipse Dixon by 0.224s.
With eight minutes to go, Helio Castroneves spun the Meyer Shank Acura on pit exit, temporarily causing a red flag as he recovered on the grass. The #60 was assessed a penalty – stop and loss of five minutes of running time – for driving the wrong way in pitlane.
Yelloly continued to impress and wound up third fastest, 0.432s from Sims’ benchmark.
There will be a 20 minutes GTP-only session at 6:25pm local time (11:25pm GMT) this evening.
In LMP2, Mikkel Jensen set top time in the class with a 1m38.052s, the #11 TDS Racing surviving an incident with the GTD Pro Corvette, in which Jensen’s partner Steven Thomas was adjudged blameless.
Ben Hanley in the #04 Crowdstrike Racing by APR entry was 0.65s slower, and just a couple of hundredths clear of Kyffin Simpson in the Tower Motorsports entry that he’ll share with Scott McLaughlin, Josef Newgarden and John Farrano.
Then Oliver Jarvis jumped the Era Motorsport car into second, but still almost 0.6s away from top spot.
Jarett Andretti topped the LMP3 class with a 1m43.191s in the Andretti Autosport Ligier to jump ahead of the strong AWA Racing Duqueines of Moritz Kranz and Nico Varrone, and the JDC Miller MotorSports Duqueine of Luca Mars.
In the GT classes, as has been the theme throughout practice sessions at the Roar Before the 24 and then again this week, the Mercedes-Benz AMG GT3s looked very strong.
Mikael Grenier’s Team Korthoff Motorsports topped all the GT3 cars, with Jules Gounon’s WeatherTech Racing Benz topping the GTD Pro.
But Romain Grosjean produced a lap only 0.3s slower in the Iron Lynx Lamborghini Huracan, and the line-up of he, Andrea Caldarelli, Mirko Bortolotti and Jordan Pepper is looking like a real threat.
Behind them, Owen Trinkler in the TGM/TF Sport Aston Martin Vantage was just ahead of Axcil Jefferies in the SunEnergy1 Racing Mercedes, and Katherine Legge’s Gradient Racing Acura NSX.
Daytona 24 Hours - FP4 results
Source: Autosport