Indianapolis — Less than an hour after watching one winning streak end Saturday, Kyle Busch started working on another.

Now the two-time defending Brickyard 400 champion is in the best possible position for an unprecedented three-peat at Indianapolis.

Busch became the first Cup driver in nearly two decades to win back-to-back Indy poles by saving his fastest lap for the final one of the day. His speed of 187.301 mph was almost a mph faster than second-place Kevin Harvick and was the second-fastest pole-winning speed in the race’s 24-year history.

“Obviously, we’ve had a really fast car,” Busch said after winning his fourth pole of the season. “We’ve been focused on race trim and I felt like we did a pretty good job with that. But I wasn’t sure about qualifying. So, obviously, they were listened to what our teammates had to say.”

He couldn’t quibble with the results.

Harvick’s No. 4 Ford was second at 186.332 and Jamie McMurray, in the No. 1 Chevrolet, wound up third at 186.274. Nobody else topped 185.

If the 2015 Cup champion wins Sunday, he will join former Formula One star Michael Schumacher as the only drivers with three straight Indy wins in the premier series of their respective leagues. Schumacher won the U.S. Grand Prix four consecutive times on the road course. Nobody has ever won three straight races on Indy’s oval.

“We’ve just got to keep it there, stay up front and, of course, lead the last lap,” Busch said as his 2-year-old son, Brexton, giggled into a microphone.

For Busch, it was another marathon session on another hot, humid midsummer afternoon in the No. 18 Toyota.

He drove in both of the morning’s Cup practices, qualified for the NASCAR Xfinity Series race in the early afternoon and watched his four-race Indy winning streak snapped after a late pit stop dropped him from first to 21st. Busch finished 12th.

After about a 30-minute break, he was back in the car for three more qualifying rounds. His last lap allowed him to join Jeff Gordon (1995-96) and Ernie Irvan (1997-98) as the race’s only back-to-back pole winners.

It certainly wasn’t strategy.

“When you’re in such a short window, five minutes, you couldn’t come back and get the tires cooled in time to make another lap,” he said.

But it was good enough.

Harvick, meanwhile, found the consistency he was seeking but avoided going too hard to get into trouble.

“I think that was the right approach,” Harvick said. “I’ve tried to get too much in the last round and this is just not the place where you can overdrive the entry and make up for something. The problems compound fast here, but it’s good to have that speed.”

For the second consecutive week, series officials threw out a qualifying speed.

This time, it was BJ McLeod who drew the penalty after a post-qualifying inspection showed the No. 51 car had taped shut a cooling aqueduct. It was supposed to remain open and the penalty cost McLeod five spots on the starting gird.

He will start from the back of the 40-car starting grid after initially qualifying 35th with a speed of 176.294.

Kyle Larson’s pole-winning run was disallowed last week at New Hampshire.

Byron wins Xfinity race

William Byron’s first trip to Indianapolis Motor Speedway ended with an unforgettable finish.

After taking the lead with 15 laps left, the teenage rookie used some savvy moves and a little luck to hold off the hard-charging Paul Menard for his third NASCAR Xfinity Series win in less than a month. The margin of 0.108 seconds was the narrowest in race history, and he did it by successfully blocking the 2011 Brickyard 400 winner for the final two laps while dealing with a troublesome tire for the final 20.

“I can’t believe that tire held,” Byron shouted after the postrace celebration. “But it is awesome, man.”

At 19 years, 7 months, 23 days, Byron became the youngest winner of a major race on Indy’s historic 2.5-mile oval. Brazil’s Matheus Leist set the previous mark in May when he won the Indy Lights race at 19 years, 8 months, 19 days.

And in three short weeks, Byron has visited victory lane at two tracks — Daytona and Indy — that often torment more experienced drivers.

Getting there Saturday sure wasn’t easy.

Byron and the series’ other drivers used restrictor plates, new air ducts and a different splitter in hopes of making the race more competitive than in past years. In part, it worked.

Eight drivers traded the lead 16 times, both race records. And before Menard pressed the issue, Byron had to hold off Joey Logano, who finished third more than three seconds back.

“I made a pretty aggressive dive into (turn) one on the last lap to see if I could get him loose but he hung on,” Menard said. “Maybe I could have gotten his bumper but it would have killed my momentum too. I definitely tried to get him loose and couldn’t.”

NHRA qualifying

Leah Pritchett took the No. 1 Top Fuel qualifying position in the Mopar Mile-High NHRA Nationals at Bandimere Speedway.

Pritchett set an elapsed-time track record with a 3.733-second pass at 326.24 mph during the fourth and final qualifying session. She has four No. 1 qualifiers this year.

Courtney Force topped Funny Car qualifying, Drew Skillman took the No. 1 spot in Pro Stock, and Eddie Krawiec was the fastest in Pro Stock Motorcycle.

Force set both ends of the track record with 3.889 at 328.30 in a Chevrolet Camaro SS during the first qualifying session Friday. Skillman had 6.924 at 198.29 in a Camaro during his second and final pass of the day, and Krawiec ran a 7.178 at 187.29 on a Harley-Davidson in his first pass Saturday.