Alonso now only needs to score one point in the final Grand Prix race of the season at Brazil's Autodromo Carlos Pace track to secure the title, while Schumacher's only chance of winning is to come first in the race at Interlagos with Alonso not scoring at all.
"Anything can happen, the same in Brazil, who knows - we have to go there and play safe and we have to finish the race," Alonso said.
"When the gap behind Michael was only around 5.8 or 5.9 or six seconds, I thought it was possible to win the race. Why not? I thought.
"Then it was completely a surprise when I saw what happened to Michael. Ferrari don't have many mechanical problems, so that was a big surprise for me," added the Spaniard.
"But the races are long and you know you have to finish. These points are important, but as we all expected the championship will not be decided until the last race, in Brazil."
Schumacher's Ferrari teammate Felipe Massa finished second, while Alonso's teammate Giancarlo Fisichella finished third to end an emotional week for the Italian whose best friend died on Thursday.
"He was my very best friend so this was not an easy race for me at all, mentally or psychologically," said Fisichella who wept openly on the podium after the race.
25-year-old Alonso trailed Schumacher for 36 laps of the 53-lap race before the German driver suffered an engine failure for the first time this year, opening the way for the defending champion to take the lead and eventually win.
The Brazil Grand Prix at takes place at Interlagos on October 22.