The Spaniard put Renault on the podium in the season-opening Australian Grand Prix after a lonely race to third place behind the two Ferraris.
"I was too slow to fight with the Ferraris and I was a little bit quicker than Jenson (Button) and the Williams and I was in the middle of nowhere," he said.
"From the first lap it was impossible to keep close behind Rubens (Barrichello) and I had no-one in my mirror and I had 58 laps like that."
Alonso, who last year became the youngest driver to win a Formula One race at the age of 22, roared off the grid with a sensational start that catapulted him from fifth to third.
With two wheels on the grass, he went past the Williams of Colombian Juan Pablo Montoya and Button's BAR before pulling away.
It was impressive stuff from the Spaniard and confirmed that Renault's progress in testing was real.
Schumacher, the six-times world champion who notched up his 71st win on Sunday, did not hesitate when asked whether Alonso could fight for the title.
"I think he is in the perfect position. Honestly, he has a strong car, they're very quick, very consistent," he said. "And he's alright as a driver."
Alonso said the podium was a pleasant surprise for a team that finished fourth overall last year but has targeted wins and a top-three placing in 2004.
"We came here with a good car, we knew that," he told a news conference. "But we have three or four steps coming on the engine in the European races and I think we can be competitive at that time.
"For us, the target in the first three or four races will be to take points and this podium is much better than we expected at the beginning.
"To be on the podium in front of Williams and McLaren is a little surprise for us. It was a tough race."
The Spaniard easily built up a 30-second gap to Button, fourth for much of the race, but found himself 30 seconds behind Ferrari runner-up Barrichello.
With new regulations forcing drivers to stick with the same engine all weekend, Alonso eased off to ensure the podium finish.
"I think all the teams were a little bit conservative and tried to score their first points and finish the first race," he said. "We will find out in Malaysia if we can fight for something more."
The Malaysian Grand Prix is next and Alonso was impressive there last year, becoming the youngest driver to start a race on pole position.
