Spain's Alejandro Valverde of Team Movistar made an emotional return from a two-year doping ban by winning the fifth and longest stage of the 2012 Santos Tour Down Under earlier today, closing in on overall victory in the first event of the 2012 UCI WorldTour.

Valverde outsprinted Team GreenEdge's Australian Simon Gerrans - a stage winner on the Tour de France, Giro d'Italia and Vuelta a Espana - to claim the 151.5 kilometer (95 mile) stage which finished with a gruelling climb to the summit of Old Willunga Hill.

Gerrans will wear the tour leader's ochre jersey in Sunday's final stage - a 90 kilometer race around a street circuit in downtown Adelaide - but there is no time difference between him and Valverde, meaning a countback may be needed to decide the winner.

Australia's Gerrans has the race lead entering the final stage because he has a lower aggregate placing than Valverde for the first five stages.

Valverde leaned across the handlebars of his bike and sobbed after winning Saturday's stage from McLaren Vale to the top of Old Willunga Hill, the first time in the race's 14-year history the stage has finished on its highest summit.

"This win is for everyone who has supported me during my time off," Valverde said. "It's a perfect comeback for me.

"We targeted this stage as a team because we thought it suited may abilities and that's how it worked out," Valverde said.

The 31-year-old Valverde was banned for two years from January 2010 after being implicated in Operation Puerto, a blood-doping ring in Spain involving more than 50 riders. He gave up the No. 1 world ranking in the process.

While he never tested positive for a banned drug, Valverde was reported to have been linked to the doping ring by DNA evidence seized in police raids in 2006.

The Tour Down Under is his first race since the ban ended and provided a reminder of his ability as he sets his sights on the Tour de France in June.

Switzerland's Martin Kohler of Team BMC Racing took a 2 second lead on general classification into Saturday's stage which involved two steep and winding climbs up Old Willunga and which has often been the defining stage of the tour. He led Australia's Michael Matthews and Spain's Oscar Freier by that 2 second margin while only 9 seconds separated the tour's top 10 riders.

The stage completed reshaped the overall standings.

Six riders, including Australian veteran Stuart O'Grady, made a breakaway early in the stage and led by up to 8 minutes. They were gradually pulled back by the peleton and young Australian Nathan Haas was the last of the group to be caught after reaching the summit first on the first climb up old Willunga.

World under-23 champion Rohan Dennis of Australia, still an amateur, and Valverde's teammate Javier Moreno broke away on the second 3-kilometer climb to Old Willunga's peak.

Moreno rode almost to exhaustion to drag Valverde into the race and the Spanish star was able to ride around Gerrans' wheel on the last corner to cross the line barely a meter ahead.

The final stage, in leafy parklands near the Torrens River and Adelaide Oval cricket ground, seldom results in a decisive breakaway and is likely to end with most of the 131 riders in the peleton on or around the same time.

That would result in only the second countback in the race's history and the first since 2003. Gerrans, the 2006 Tour Down Under champion who won the Australian road racing championships earlier this month, is strongly placed to win on countback.

He has finished 35th, third, 20th, 17th and second on the race's previous stages while Valverde has finish 58th, fourth, 54th and 33rd.

On Sunday's flat stage, Valverde is unlikely to be able to achieve the time advantage over Gerrans that he needs to win the tour on general classification.

"It's a great consolation prize," Gerrans said of finishing second on the stage but taking the overall lead. "It will be a box ticked if I'm still wearing this jersey at the end of the stage tomorrow."