Earnhardt entered the last lap with the lead and Keselowski on his bumper. When Earnhardt's No. 88 Chevrolet began sputtering on the back straightaway, Keselowski's No. 2 Ford shot past him for the victory in the Kobalt 400.
It was a weekend sweep in Las Vegas for Keselowski, who also won Saturday in NASCAR's second-level Nationwide Series.
"We needed to put pressure on Dale and not let him into fuel-saving mode," Keselowski told a television audience. "We're very happy."
Earnhardt, who won the season-opening Daytona 500, knew he was in danger of running out of fuel. During a caution period with 47 laps left in the 267-lap race, his team opted for him to stay out of the pits and not refuel.
"Running out of gas, that's tough," Earnhardt said. "It's no shock to us that we ran out. We knew we were short."
Still, it was Earnhardt's third top-two finish of the season. After his Daytona 500 win, he finished second last weekend in Phoenix.
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