Sergio Perez on Monaco GP qualifying crash: I can't believe what I've done

MONACO - Sergio Perez said he is braced for a nightmare Monaco Grand Prix after crashing out of qualifying, a moment which could be pivotal in this year's title race.

Just 12 months on from winning the famous race Perez, Red Bull teammate Max Verstappen's only realistic title challenger this year, faces the prospect of starting from last at a circuit where overtaking is close to impossible.

"It's an unbelievable day," Perez, who trails Verstappen by 14 points in the championship, told reporters shortly after the crash. "I cannot believe what I've done."

Verstappen will start the race from pole position after a stunning late Q3 lap saw him edge out Aston Martin's Fernando Alonso, making the frustration even bigger for the Mexican driver.

"I knew that today we could have had a shot at pole but I didn't drive to my level so that's why I'm here," he said.

Perez said he was just pushing too hard and was caught out by how the rear of the car slipped from underneath him.

"It just caught me by surprise. Just getting that rear out of shape, especially really late into the corner. That really caught me out. There was nothing else I could do because it was really late in the corner -- I could not cut the corner or go out of the corner. It's how it is sometimes."

At some circuits, starting at the back can encourage a more aggressive pit-stop strategy to move up the order, but Perez admitted he does not have high expectations for this grand prix.

"It's just going to be a nightmare tomorrow. I do expect a very difficult race. Whatever you do, people just cover you and you end up in the same position pretty much."