Updated

By Mark Gleeson

RUSTENBURG (Reuters) - The United States and Ghana went into extra time at the World Cup on Saturday with their second round knockout game level at 1-1.

A fifth minute goal from Kevin-Prince Boateng sent Ghana into an early lead but the Americans fought back strongly after a sluggish first half, equalizing just after the hour mark with a Landon Donovan penalty that went in off the post.

German-born Boateng, who qualified to play for Ghana on the eve of the finals, stole the ball from Ricardo Clark in midfield and ran on to fire home from the edge of the area in a perfect start for Africa's last representatives at this World Cup.

They might have had a second in the 37th minute but Tim Howard saved a powerful angled shot from Kwadwo Asamoah.

At the other end, key stops from goalkeeper Richard Kingson kept Ghana's lead intact against a U.S. side showing the effects of two tough previous matches.

Kingson saved a shot from Robbie Findley with his legs 10 minutes before the interval and made a one-handed stop to deny substitute Benny Feilhaber at the start of the second half.

A tactical switch by U.S. coach Bob Bradley strengthened the midfield and allowed his side to assume command, pegging Ghana back in the second half.

Ghana's teenage defender Jonathan Mensah gave away a 62nd minute penalty when he brought down Clint Dempsey.

Donovan struck his spot kick in off the post to give the Americans a deserved equaliser as they suddenly found the energy to stage what is now becoming a customary second half rally.

Jozy Altidore then hacked the ball narrowly wide 10 minutes from time after getting the better of the Ghana defense.

The winners, after 30 minutes of extra time and possibly a penalty shootout, will face Uruguay in the quarter-finals.

(Editing by Ken Ferris)