ABETONE, Italy (AP) Alberto Contador claimed the overall lead in the Giro d'Italia after the first mountain stage on Wednesday, as the race favorites leaped into action on the concluding climb to Abetone.
Jan Polanc, a 23-year-old Slovene with the Lampre team, won the fifth leg.
Polanc got in an early breakaway and attacked on the final climb - 17 kilometers (10.5 miles) at an average gradient of 5.4 percent. He clocked little more than four hours over the 152-kilometer (94-mile) stage across central Italy, which started in La Spezia.
French veteran Sylvain Chavanel, another breakaway member, finished second, 1:31 behind, and Italian title hopeful Fabio Aru crossed third with the same time, with Contador and Richie Porte right behind.
In the overall standings, Contador is two seconds ahead of Aru, with Porte 20 seconds behind in third.
Previous leader Simon Clarke dropped far behind.
A two-time Tour de France champion, Contador won the Giro in 2008 and was also triumphant in 2011 but was stripped of that title for testing positive in the 2010 Tour.
''There's still a long way to go,'' Contador said. ''This was just an aperitivo.
''My attack wasn't planned. I felt good, looked around, and went,'' Contador added. ''I'm happy with the situation after five days. I didn't expect the pink jersey, but to have it is always fantastic. ... Although the one that counts is the pink jersey in Milan, so if someone else takes it tomorrow, it won't be a problem.''
Contador was the first of the overall contenders to attack on the climb and Aru and Porte quickly followed. Aru won a sprint for third, which carried a four-second bonus.
''I'm happy to be in this battle,'' Aru said. ''They're great champions and being among them is unbelievable.''
Stage 6 on Thursday is a 183-kilometer (114-mile) leg from Montecatini Terme to Castiglione Della Pescaia featuring flat sections at the start and finish and hills in between.
The 98th Giro ends May 31 in Milan.