Peter Sagan of Slovakia produced a late burst of speed to win the grueling fourth stage of the weeklong 2012 Tirreno-Adriatico race earlier today, while 40-year-old American Chris Horner took the overall lead.

Sagan clocked a marathon-like 7 hours, 24 minutes, 50 seconds over the 252-kilometer (156.6-mile) leg from Amelia to Chieti, which featured a short but steep uphill finish.

Roman Kreuziger of the Czech Republic crossed second and Sagan's Liquigas teammate Vincenzo Nibali was third, both with the same time as Sagan.

Danilo Di Luca, the 2007 Giro d'Italia champion, was fourth, and Horner, who rides for the RadioShack-Nissan team, was fifth.

The stage was meant to feature another significant climb but snow and ice on the Lanciano Pass forced organizers to create an alternate route. Still, the steep finish featured two extremely difficult sections, one at grades of 14 to 19 percent for 400 meters and the other 350 meters at 15 percent.

Nibali broke away with about 400 meters to go and when Di Luca was about to chase him down, Sagan then rushed in front.

"I was the team's reserve but I got to try also today," said the 22-year-old Sagan, who earned his second victory of the season. "The last climb was very tough but I felt great today."

Horner now holds a seven-second lead over Kreuziger in the overall standings, with Cameron Meyer of Australia third, 13 seconds back.

"The legs are good, so certainly I have a shot at winning," Horner said.

Previous leader Matthew Goss of Australia fell behind on the penultimate climb.

Seven riders broke away at the start of the stage and gained a 10-minute lead at one point. The last remaining rider in the breakaway, Pavel Brutt of Russia, was caught by the main pack with 12 kilometers (7.5 miles) to go.

Stage 5 Sunday is another difficult leg featuring two difficult climbs and another uphill finish following a 196-kilometer (121.8-mile) route from Martinsicuro to Prati di Tivo.

The race ends Tuesday with a 9.3-kilometer (5.78-mile) individual time trial in San Benedetto del Tronto, on the Adriatic coast.

Many riders use the race as a warmup for the Milan-San Remo, the season's opening single-day classic next Saturday.

Watch video highlights from every stage of the 2012 Tirreno-Adriatico in our video section.