Phelps on the brink of Spitz seven

Michael Phelps of the U.S. looks at the scoreboard after swimming in the men's 200m individual medley final at the National Aquatics Center during the Beijing 2008 Olympic Games August 15, 2008.

BEIJING (Reuters) - Michael Phelps reaches for his seventh Beijing gold medal on Saturday to match the prodigious feat achieved by Mark Spitz in 1972.

Phelps goes into the 100 metres butterfly final knowing victory would put him on the same seven-gold pedestal as Spitz and bring him a $1 million bonus from his sponsors.

It would also keep him on track to exceed Spitz's Munich achievement with an unprecedented eighth gold in the medley relay on Sunday after a second-string U.S. quartet made sure they were not disqualified by a premature take-over in Friday evening's heats, as they were at last year's world championships.

World records have accompanied every step for Phelps and one more in the 100 butterfly would also match the individual count of 26 achieved by Spitz.

Phelps is both Olympic and world champion in the 100 butterfly but victory is far from assured in the only one of his five individual events in which he did not come to Beijing with the world record.

Serbia's Milorad Cavic was fastest in the heats and semi-finals, although Phelps raced his semi-final barely five minutes after the victory ceremony that marked his triumph in the 200 individual medley final and was a mere 0.05 seconds slower.

World record holder Ian Crocker, who beat Phelps to win the world title in 2003 and 2005, will also want to spoil the party for Phelps, who scored the tightest of last-gasp victories over him at the 2004 Olympics (0.04 seconds) and 2007 worlds (0.05).

Phelps turned on the power in a surging finish in the semi-finals after lagging sixth at the turn.

"It's definitely tough. Milorad and Ian having good semis, it's going to be a good race. I'll do everything I can to get out faster. If I'm there at the first 50 I'll be there at the finish," Phelps said.

Alain Bernard and Eamon Sullivan lock horns again in the men's 50 freestyle final after the Frenchman edged out the Australian world record holder in the 100 freestyle final.

But Brazil's Cesar Cielo Filho goes into the final with fastest semi-final time of 21.34, just 0.06 seconds outside Sullivan's world record.

Zimbabwe's Kirsty Coventry, frustrated at having won three silver medals but no gold, takes a final tilt at Beijing gold when she defends her 200 backstroke crown, buoyed by the fastest semi-final time.

Britain's Rebecca Adlington, winner of the women's 400 freestyle, aims for a second gold in the 800 freestyle final after posting the fastest heat time on Thursday.