Simoni won in 2003 on the only other occasion the Giro came to this mountain, and he repeated the feat on Wednesday. After chasing down the last remaining members of the day's breakaway group, he and team-mate Leonardo Piepoli moved away from Andy Schleck over the final 300 metres of a climb ranked by many as the toughest in Europe.

Despite being dropped six kilometres from the finish, Di Luca kept his composure, and managed to limit his time losses to just 31 seconds on the leaders.

He now holds a 2'24" advantage over Schleck, with Simoni four seconds further back. Saturday's 43 kilometre time-trial from Bardolino to Verone remains the only real obstacle now between Di Luca and his first Giro d'Italia victory.

After an early, short-lived breakaway from the trio of Eric Berthou, Jurgen van den Broeck, and Elio Aggiano, a dozen riders successfully jumped clear of the peloton after 25 kilometres, including world champion Paolo Bettini and Fortunato Baliani, both of whom have featured frequently in such attacks over the past few days.

Danilo Di Luca's Liquigas squad, together with the Saunier Duval team, ensured the gap between the 12 escapees and the main pack never ventured far over the five-minute mark.

With the peloton slowly closing and Carlo Naibo having been dropped along with Irizar Aranburu, Dario Cioni decided to attack from the breakaway after the summit of the second-category Tualis, and was immediately joined by Baliani and Massimo Codol.

They were unable to preserve their advantage though, and were reeled back in by the other seven members of the group.

As they tackled the first few metres of the formidable Zoncolan climb, Reading-born Italian Mario Cioni appeared the freshest of the leaders, and he attacked with gusto over the bottom half of the ascent.

The main field was dropping increasing numbers of riders as it made ground on those further up the road, and was eventually whittled down to an elite group over six, composed of Di Luca, Schleck, Piepoli, Simoni, Damiano Cunago and Riccardo Ricco as the gradient steepened. Eddy Mazzoleni, who before the stage lay second overall, fell behind three kilometres into the climb.

Ricco was the first to be dropped, and with Di Luca visibly beginning to suffer, Simoni decided to go on the attack. He gradually moved away, though was unable to build up any significant lead, and within minutes was caught by Schleck and Piepoli, with Cunego and Di Luca unable to keep the pace.

In front, Cioni ran out of steam and was passed by Codol, who in turn was caught by Simoni's trio two kilometres before the summit.

Di Luca refused to panic though, and, riding at a constant rhythm, made back a few seconds lost on Cunego to join forces with the Lampre man.

While Simoni and Piepoli burst clear of Schleck with the finish line coming into view, Di Luca ensured he fell no further behind his two main rivals, and rolled across the line in fourth position, just over half a minute in arrears.

Schleck's time-trialling ability ensures he will become "the Killer's" main threat over the rest of the race, though with an advantage of 2'24", only a huge surprise would prevent the Liquigas man wearing pink atop the podium in Milan.

MF