James leaned across the line yesterday to win the gold medal in the 400 meters at the world championships, upstaging the reigning titleholder, who had to grab the back of the teenager’s jersey to avoid falling.

The surprise finish put Merritt on notice: There’s a new kid in the blocks, and he’s pretty good. He’s even drawing comparisons to Jamaican sensation Usain Bolt.

“I don’t want to be the next Usain Bolt,’’ said James, who turns 19 tomorrow. “I’m happy in my own skin.’’

Merritt was a little rusty. This was his first major meet since serving a 21-month suspension for using a banned substance that his lawyer said was the result of a male-enhancement product. He lost steam with about 10 meters to go, opening the door for James.

“He is a great competitor,’’ Merritt said as the Americans failed to win gold in the 400 for the first time since 2001.

Their next major meeting could come at the London Olympics. Provided, of course, Merritt is allowed to compete.

The Court of Arbitration for Sport will deliver a verdict on the IOC’s “six-month rule,’’ which took effect in 2008 and prevents athletes who receive doping bans of more than six months from competing at the next Olympics. A decision is expected next month.

The only real surprise of the night came when pole vaulter Yelena Isinbayeva of Russia failed to win a medal in her third straight global championship. That’s after a run of seven titles in a row spanning the Olympics along with world outdoor and indoor competitions.

That gave Fabiana Murer the gold.

Other winners included Robert Harting of Germany (discus), Yuliya Zaripova of Russia (steeplechase), Tatyana Chernova of Russia (heptathlon) and David Rudisha of Kenya (800).

Cuba’s Dayron Robles said he wouldn’t have been disqualified from the 110-meter hurdles at the world championships if he came from a more powerful country.

Robles was stripped of his first-place finish in the hurdles in South Korea Monday after judges upheld an appeal claiming he held back Chinese runner Liu Xiang.

“If I were from another country that had more power, that wouldn’t have happened,’’ Robles told the AP in an e-mail. “It’s very controversial that these things happen in an athletics world championships, lamentably it was my turn to lose out,’’ Robles said.