Contador holds on to four-second lead

(CNN) -- Emanuele Sella recorded his third mountain stage of this year's Giro d'Italia on Saturday, and Alberto Contador held onto his slim overall lead for a sixth day.

Sella broke away from a group containing all the top contenders 19 miles from the finish and finished the 224-km (139-mile) 20th stage in 6 hours 52 minutes 45 seconds.

Gilberto Simoni was 1:04 behind, followed by Joaquin Rodriguez Oliver a further 18 seconds adrift.

The riders climbed the Mortirolo, the toughest ascent of the Giro this year for its combination of length and steepness. Sella waited to attack until the last climb, the relatively easy Aprica.

Contador finished 1:30 behind Sella -- the same time as Riccardo Ricco and Marzio Bruseghin -- and has an overall time of 89 hours, 23 minutes, 25 seconds. Contador has a 4-second lead over Ricco and 2 minutes over Bruseghin who is third.

The Giro concludes Sunday with a 28.5-kilometer (17.7-mile) time trial that finishes in Milan.

"Today was another tough day," Contador said. "We have to wait until tomorrow before I can celebrate, this is not over yet."

Contador, who won last year's Tour de France, has generally been stronger than Ricco at time trials. Bruseghin is strong at time trials and has won one already in this Giro, but it will be difficult for him to make up two minutes in the relatively short course.

"It's clear that Contador is much stronger than I am at the time trials, but I will give my best effort," said Ricco, who at 24 is one of the Giro's youngest riders.

"Maybe Contador will have a tough day. After all we are not robots and in the Giro one bad day can happen to anybody."

Danilo Di Luca, last year's Giro winner, finished more than five minutes behind Sella and dropped out of contention after entering the stage in third place and 21 seconds behind Contador.

The Italian rider had attacked Friday and made up two minutes in the standings.