HARTFORD, Conn. (AP) — Donnell Whittenburg is working hard to win his first national title and make his first U.S. Olympic team.

The 21-year-old used a steady performance Friday to post 89.9 points and take the all-around lead after the first day of the of the U.S Gymnastics Championships, a fraction of a point in front of three-time defending national champion Sam Mikulak.

Eleven men, including Mikulak and three other members of the 2012 Olympic team, were within three points of the lead.

"It definitely focuses on the depth of our group," said Whittenburg, who was second last year in the national championships. "We have so many great guys competing here. Anyone can take the top spot."

Whittenburg took the lead after a stumble by Mikulak, who led after the first five of the six rotations. The 23-year-old is back from an Achilles injury that kept him out of last fall's world championships. He seemed to be in control and broke into a big smile after sticking the dismount on his parallel bar routine in the fourth rotation.

But Mikulak had had a tough final performance, stumbling in the middle of his floor routine and then stepping out of bounds on the final tumbling run. He finished with 89.85 points and heads into Sunday with a chance to become the first to win four national titles in a row since Blaine Wilson won five straight in the 1990s.

"It's not how you want to end the first day," Mikulak said. "But, I've got another day to actually show how well I can do."

Whittenburg started slowly with a 13.8 on the pommel horse, but impressed after that, with a 15.95 on the rings and a 15.2 on the vault.

Five gymnasts are within a point of him. Chris Brooks was third at 89.5, and Jake Dalton finished fourth with 89.4 points. Yul Moldauer, the NCAA champion from Oklahoma, was fifth at 89.25, followed by Stanford's Akash Modi at 89.15.

Eighteen men will be chosen from this competition to compete in the Olympic trials later this month in St. Louis, where they will vie for spots on the five-member Olympic team competing in Rio in August.

Besides Mikulak and Dalton, former Olympians John Orozco (87.4 points) and Danell Leyva (86.9) remain in striking distance for the all-around national title.

Two-time Olympian Jonathan Horton missed the championships and will miss the Olympics with a shoulder injury suffered early this year.

Dalton, who also missed the world championship team last fall after undergoing shoulder surgery, led the competition after the first three rotations. But he fell back after a poor routine on the pommel horse, which had a lower degree of difficulty than many of his competitors.

Orozco, coming back from a second torn Achilles, also had a tough time on the horse, spinning off in his routine during the first rotation. The 2012 national champion was forced to play catch-up the rest of the night.

Leyva, who won the all-around bronze in London, competed with a heavily wrapped left leg after being bitten last month while trying to break up a fight between his family's two English bull dogs. He said the injury did not hamper his performance, which included a fall from the high bar.

"The leg felt strong," he said. "On high bar, I couldn't tell you what happened exactly. I went to grab the bar and my grip hit it instead of grabbing it smoothly."