Maldonado gave Williams its first Formula 1 victory since the 2004 Brazilian GP as he resisted pressure from Ferrari driver Alonso at various stages to win at Catalunya.
"It was so close. We were looking to manage the tyre degradation so I couldn't push that hard, just to keep the tyres alive for the end of the race and Fernando got very close," said Maldonado.
"There were some moments where he was so close especially at end of the straight, but I was managing the gap and controlling everything.
"Our pace today was very strong, the car was fantastic, so was the team. We did a small mistake at the last pitstop but it did not affect our performance."
Maldonado said the car underlined how much progress had made since last season, when it endured its worst ever campaign and scored a mere five points.
"I think it's a wonderful day, unbelievable for me and all the team," he said. "We have been pushing so hard since last year to improve race by race and here we are.
"It was a tough race because of the strategy as well, it was hard especially because of rear tyres, after a couple of laps we were struggling with them, but I need to say I am pretty happy because car was so competitive since the first lap."
The Venezuelan has been strong in Monte Carlo - venue for the next grand prix in a fortnight - throughout his career, and acknowledged that expectations for the next race would now be high.
"It will be a great opportunity for us to be strong again," said Maldonado. "We need to keep continuing like that to develop it as soon as possible. Consistency will be the most important thing in this championship."