Lewis Hamilton tops wet practice at US Grand Prix

AUSTIN, Texas (AP) Lewis Hamilton slipped and skidded around the Circuit of the Americas, then retreated to the Mercedes garage.

That's where he could stay dry, watch the weather radar and plan for what he hopes will be a final charge to the Formula One championship at the United States Grand Prix.

Hamilton posted the fastest time in Saturday's final practice session as another day of harsh weather pounded the track with torrential rain. Then he and other drivers waited through a three-hour delay before race officials postponed qualifying until a rare Sunday morning session before the scheduled afternoon race.

For Hamilton, that means not knowing yet if he'll start from pole position on the track where he has won two of the last three years. Another win Sunday could clinch his second world title in two years and third overall.

''Hopefully, the weather will back off a bit,'' Hamilton said ''Let's hope for a better day. Sunshine would be great.''

Sunday will be just the fourth time since 2004 and first since 2013 that Formula One has used race-day qualifying.

The 30-year-old Hamilton won his first world championship in 2008 driving for McLaren. His recent domination with Mercedes has already claimed 20 victories and nine other podium finishes the past two years with four races left this season.

Hamilton has a 66-point lead over Ferrari's Sebastian Vettel in the driver standings. He'll win the championship if he outscores Vettel by nine points and Mercedes teammate Nico Rosberg by two.

Vettel posted the second-fastest time in Saturday's soggy practice. But while still mathematically in the title hunt with four races left, his chances of pushing it to Mexico City next week took a hit when Ferrari fitted his car with a fifth engine, one over the season limit. That drew a 10-spot grid penalty for Sunday's start.

Vettel, who has three wins this season, said there were no regrets about using the engine and absorbing the penalty, calling it something we ''had to take.''

''We have a chance to qualify well and minimize the damage,'' Vettel said.

The worst of the weather is supposed to start clearing Sunday morning. But it could still be raining when the drivers return for a 9 a.m. qualifying start, five hours before the race.

If rain continues to swamp the track in the morning, a potential option would be to use Saturday's practice times to set the starting grid. That would put Hamilton on the pole with Sahara Force India's Nico Hulkenberg sitting second and Williams' Valtteri Bottas third.

Hulkenberg, whose has one career pole position in 92 races, said qualifying and racing the same day could be difficult.

''It will be a busy day, but it's got to work,'' Hulkenberg said.

The teams clearly treated Saturday's morning practice session as a possible qualifier and kept their drivers on the track for long stretches to log laps, even as they struggled with the slick surface and difficult visibility.

''No complaining. Safe enough to run,'' Red Bull's Daniel Ricciardo radioed to his garage early in the session.

But the rain kept coming and the cars kept sliding off the track, Hamilton included. Several times he slid through corners or had to take his car wide off course.

Vettel found himself stopped off the track and facing backward after one spinout.

''At one point it was really good fun,'' Hamilton said. ''And then at the end it got a little bit dangerous.''