Sanchez followed an attack by Andy Schleck of Luxembourg on the last of the seven laps of the climb up the Badaling Pass
by the Great Wall and then won a six-up sprint ahead of Rebellin, who won the silver medal on his 37th birthday.
Sanchez claimed Spain's first gold medal in any Olympic Games Cycling Road Race.
Heat and humidity took a brutal toll on the peloton. Of the 143 starters, only 90 finished.
The longest Cycling Road course in Olympic Games history at 245km started at 11:00 under partly cloudy skies with high
humidity in front of the Yongdingmen Gate in the south of downtown Beijing.
Temperatures hovered around 26 degrees Celsius but humidity was 94 per cent at the start, creating extremely difficult
conditions for the race.
Patricio Almonacid of Chile and Horacio Gallardo of Bolivia escaped in the opening 5km of the course and built up a gap
of more than 15 minutes as the main pack rode slowly over the first hour of racing over relatively flat roads through central
Beijing. The pair would eventually fade out of contention and neither finished the race.
A potentially dangerous group of 26 riders extracted themselves from the main pack about 60km into the race before hitting
the first of seven loops of a 23.8km circuit that included a steep climb up by the Badaling section of the Great Wall.
With five laps to go on the circuit, the lead group nursed a dangerous lead of 5:10 minutes. Jason McCartney of the United
States and Vladimir Efimkin of Russia went to the front of the chasing main pack to trim the gap to within three minutes.
With four laps to go, Italian Vicenzo Nibali ramped up the tempo in the chasing pack for the favored Italians to bring
the peloton within striking distance of the leading group going into the final, decisive laps.
Johan Vansummeren of Belgium, Marcus Ljungqvist of Sweden and Rigoberto Uran of Columbia bridged out to Aliaksandr Kuchynski
of Belarus and Ruslan Pidgornyy of Ukraine, two stragglers from the early break, but it was a short-lived move.
With two laps to go, the groups merged, but on the final lap, six riders broke away. Sanchez and Rebellin followed an attack
by Andy Schleck. The trio opened up a 30-second gap on a lead group of chasers.
Cancellara, Alexander Kolobnev of Russia and Michael Rogers of Australia bridged up on the final descent and the six roared
into the finish line to fight for the medals.
Pre-race favorite Alejandro Valverde of Spain chose not to chase down his teammate and came across the line 13th at 22
seconds back.
Defending Olympic champion Italian Paolo Bettini crossed the line 18th at 1:10 back.
Tour de France winner Carlos Sastre of Spain rode as a worker for the Spanish team and finished 49th, 7:17 minutes back.
