Mary Schwalm, Associated Press
Alicia Sacramone competes at the U.S. gymnastics championships in Boston Thursday.

BOSTON — Boston? Beijing? The way Shawn Johnson was going, only she could tell the difference.

The reigning world champion showed she's still the one to beat Thursday night, taking a solid lead at the U.S. gymnastics championships with a score of 63.450.

Nastia Liukin, who is expected to challenge Johnson all the way through Beijing, was 1.15 points behind after posting a 17.05 on uneven bars that was the highest mark for an American woman — on any event — since gymnastics went to its new, open-ended scoring system two years ago. The finals are Saturday night.

"I definitely want to keep my title. I think it's something that everybody wants to have," Johnson said. "But that is not the most important thing. This is just a test run."

That's because nationals are only the start of a very big summer. The top 12 gymnasts at nationals, along with any chosen by the selection committee, advance to the Olympic trials, which are June 19-22 in Philadelphia. The top two at trials earn spots on the Beijing Olympic team, with the remaining four members chosen July 20 after a training camp at the Karolyi ranch.