Defending NASCAR Cup champion Martin Truex Jr. earned his first victory of 2018 after reigning supreme at Auto Club Speedway.

Truex, who started on the pole for Sunday's race in California, ran up front throughout the afternoon – winning the first two stages before claiming overall victory, his 16th career victory.

The deciding moment in the face came with 37 laps remaining, when the leaders all pitted.

Kyle Busch won the sprint off pit road ahead of Truex, but a problem immediately surfaced.

Busch's crew radioed to say they had adjusted the wedge the wrong way on the stop. Five laps later, his loose car bobbled and Truex sped into the lead for good.

"We never gave up on it," Truex told Fox Sports. "I knew we had a really good race car. … Once we got in clean air this thing was unbelievable."

"It's just unbelievable to be able to do this for a living."

Kevin Harvick, who won the previous three races and was favourite to claim a fourth straight victory in the Auto Club 400, crashed early in the first stage after running into Kyle Larson's car.

Although Harvick's crew made repairs, he returned several laps down and finished 35th.

"I went down to side draft, he was coming up and we touched," Harvick said. "I think that's my fault for coming down the race track … I was trying to get a little too much right there."

Larson overcame that early incident with Harvick to finish second. Busch crossed the line third, followed by Brad Keselowski and Joey Logano.