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Keselowski, who will start sixth in Sunday’s NASCAR Cup season-opener, led the way with an average lap speed of 191.201 mph.
Only 17 of the 40 cars in the race elected to participate in Saturday’s final 50-minute session.
“We just keep dialing in our Ford,” Keselowski said. “You know, in the Duels, we weren’t where we wanted to be. I felt like we needed to work on this thing a little bit.
“So, we spent the last two practices – this one today and of course last night – working on some things and made some really good gains to have both the speed and the handling it’s going to take to win the 500.
“We made some really good gains and super-confident going into tomorrow.”
Brad Keselowski, RFK Racing, Nexlizet Ford Mustang
Photo by: Gavin Baker / NKP / Motorsport Images
Reigning series champion Joey Logano ended up second-fastest (191.196 mph) and Ryan Blaney was third (191.180 mph). They were followed by Ryan Preece, Harrison Burton and Chase Briscoe as Fords swept the top six spots on the speed chart.
Rounding out the top-10 were A.J Allmendinger, Justin Haley, Noah Gragson and Riley Herbst.
No Toyotas elected to participate in the final session.
Among those drivers who ran at least 10 consecutive laps, Preece had the best average speed (189.316 mph). Briscoe and Burton were second and third, respectively, in that category.