After registering a 21-run win in the series opener, India slumped to a humiliating defeat in the second ODI against Sri Lanka on Tuesday.
Gambhir said Sri Lanka looked better prepared after the series against Pakistan, while the Indians were a bit rusty following two-month long break.
"We have never underestimated Sri Lanka. They are a quality side. We have never taken them lightly. It should be a very good series from now on," Gambhir said on the eve of the third ODI to be played at the R Premadasa Stadium.
With the series evenly poised at 1-1, Gambhir said the remainder of the tour will only get tougher for India from here on.
"We have done well against Sri Lanka in recent past. They have also played well against us. So, it will be tough as we know the strengths and weaknesses of each other," he said.
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He also refused to predict the outcome of tomorrow's match
"You can't predict results If people are honest and give their 100 per cent, nothing else matters," Gambhir added.
The third and fourth ODI of the series will be played at the R Premadasa Stadium here while the fifth match and the lone Twenty20 International will be held at the Pallekele International Cricket Stadium.