PHILADELPHIA - Shawn Johnson and Nastia Liukin closed on places in the U.S. women's Olympic gymnastics team by taking the two top spots on the first day of the trials on Friday.

Two places will be awarded to the top finishers when the trials end on Sunday with the other four team members to be named after next month's selection camp.

World all-around champion Johnson headed the rankings with 64.000 points after four events. Liukin, twice a U.S. national champion, followed with 63.500 points and Chellsie Memmel was third on 62.250.

Johnson was happy with her performance but admits she needs to improve on the uneven bars.

"There are three or four different things I can work on and improve for Sunday," she told reporters.

Johnson finished only third on the bars behind Liukin but the 16-year-old world champion had the best marks in the vault, balance beam and floor exercise.

Johnson and Liukin finished one-two on the floor and beam.

Johnson, forced to train at another venue after Iowa's recent flooding ruined the floor of her regular gym in Des Moines, said she was not affected by the disruption.

"I didn't want that weighing on me," she said. "I put it all behind me and had the time of my life."

Liukin also said she plans to work on her bars routine, particularly her dismount.

"I know I can add to my scores," the 18-year-old said. "The dismount was not what I was hoping for."