Grosjean was the only man able to carry the fight to the Red Bulls at Suzuka, and remained in contention for victory until the final quarter of the race, when Vettel was able to pick him off at Turn 1.
Vettel's team-mate Mark Webber later demoted Grosjean to third.
The German said that, aside from his excellent race, Grosjean deserves respect for how he has turned his F1 career around and developed into a match for his world champion team-mate Kimi Raikkonen.
"I thought it was a great day for Romain; he drove a fantastic race," Vettel said.
"I think Romain did a great job all weekend.
"We know Kimi is a strong driver. Last year Romain did some mistakes but the most important thing is that we learn from these mistakes,.
"[Romain] learned a lot of things and gradually he is improving so big respect for that."
Vettel said he was surprised he was able to go deeper into his second stint than Grosjean's Lotus, which gave him the foundation to fight back from a poor start.
"It was a horrible start but then a fantastic comeback," he said.
"They [Lotus] looked strong [but] struggled a bit more on the prime. The race favoured us over the distance, which seemed unusual compared to the Lotus.
"I managed the gaps at beginning of stints and pushed at the end. We didn't lose the patience early on and made the stints as long as possible to help us."
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