Passo dello stelvio - Belgian Thomas de Gendt put up a superb solo effort to win the fearsome Giro d'Italia 20th stage on Saturday, with Joaquim Rodriguez retaining the overall leader's pink jersey.
Spain's Rodriguez, riding for the Katusha team, finished fourth and now holds a 31-second advantage over Canada's Ryder Hesjedal going into Sunday's 21st and final stage time trial.
Despite almost doubling his lead Rodriguez will have his work cut out to contain Hesjedal in Milan with the Garmin rider favoured by the 30km race against the clock.
"Ryder (Hesjedal) is the favourite to win, I'm not saying that I can't beat him but I'm being realistic, I'm telling myself that I need a miracle," conceded Rodriguez, who nevertheless is taking comfort in the optimistic view adopted by his manager, Sebastian Webber.
"He thinks that this time trial, with quite a few bends, will suit me," said the pink jersey holder.
De Gendt's astonishing display of power on this stamina-sapping 219km alpine ride, culminating in the Category I climb up the Passo Stelvio, which at 2 757m altitude is the highest finish of any of the Tours, also pushed him into podium contention.
The 25-year-old Vacansoleil rider leapt from eighth to fourth in the general standings after crossing the snow-lined finish 55 seconds up on Damiano Cunego.
At the start of the stage de Gendt was out of contention, 5:40 behind Rodriguez, but after this fine effort he moved to within 2:18 of the leader.
Mikel Nieve took third at 2:50 with Rodriguez in fourth, 3.22 down to lift him one point above Briton Mark Cavendish in the red jersey points standings.
Defending Giro champion Michele Scarponi, fifth on Saturday, is placed third in the GC, 1:51 adrift.
Despite losing time on Rodriguez, Hesjedal did enough in sixth to give him a great chance of creating cycling history on Sunday in Milan by becoming the Tour of Italy's first ever Canadian champion.
De Gendt made his ultimately successful bid for stage glory when slipping away from the peloton 57km from the finish at a time when the pack were tackling the dreaded Mortirolo climb.
"I decided to attack on Mortirolo because I know the descent and I know it's dangerous."
With the help of a team member he maintained the pressure in the following valley to set out up the final punishing push to the Stelvio summit with a lead of almost four minutes.
He deployed his local knowledge to perfection - for the past six years he has used the mountain as a training camp.
"The last few kilometres were very tough, but I couldn't consider weakening," he added.
"It was in last year's Tour de France that I began to appreciate that I could defend myself in the mountains. This year I won't be on the Tour de France as I'm getting married..."
His virtuoso feat not only ensured his place in the memory of the 2012 Giro but also put at risk Italy's proud tradition of having a rider on the final podium for every year since 1995.
Tour of Italy results after Saturday's 219km 20th and penultimate stage from Caldes to Passo dello stelvio:
1. Thomas De Gendt (BEL/VAC) 6hr 54min 41sec, 2. Damiano Cunego (ITA/LAM) at 0:56s, 3. Mikel Nieve (ESP/EUS) 2:50, 4. Joaquim Rodriguez (ESP/KAT) 3:22, 5. Michele Scarponi (ITA/LAM) 3:34, 6. Ryder Hesjedal (CAN/GRM) 3:36, 7. John Gadret (FRA/ALM) 4:29, 8. Rigoberto Uran (COL/SKY) 4:53, 9. Sergio Henao (COL/SKY) 4:55, 10. Ivan Basso (ITA/LIQ) 4:55, 11. Domenico Pozzovivo (ITA/COG) 5:39, 12. Hubert Dupont (FRA/ALM) 5:53, 13. Ben Hermans (BEL/RSH) 7:58, 14. Gianluca Brambilla (ITA/COG) 8:32, 15. Roman Kreuziger (CZE/AST) 9:10.
1. Joaquim Rodriguez (ESP/KAT) 91h04min 16sec, 2. Ryder Hesjedal (CAN/GRM) at 0:31s, 3. Michele Scarponi (ITA/LAM) 1:51, 4. Thomas De Gendt (BEL/VAC) 2:18, 5. Ivan Basso (ITA/LIQ) 3:18, 6. Damiano Cunego (ITA/LAM) 3:43, 7. Rigoberto Uran (COL/SKY) 4:52, 8. Domenico Pozzovivo (ITA/COG) 5:47, 9. Mikel Nieve (ESP/EUS) 5:56, 10. John Gadret (FRA/ALM) 6:43, 11. Sergio Henao (COL/SKY) 7:20, 12. Dario Cataldo (ITA/OPQ) 12:14, 13. Johann Tschopp (SUI/BMC) 12:34, 14. Gianluca Brambilla (ITA/COG) 13:28, 15. Roman Kreuziger (CZE/AST) 18:09