Chasing a modest 141, the Mumbai outfit lost wickets at regular intervals to be shot out for 108 in 19.1 overs last night, thanks to the effort of the Kolkata bowlers.
West Indian off-spinner Sunil Narine was unplayable and pushed Mumbai Indians to the brink with a superb haul of four for 15.
And he was well-supported by Laxmipathy Balaji (2 for 11) and Jacques Kallis (2 for 42), while left arm spinners Shakib Al Hasan and Iqbal Abdulla too did their bit with a wicket each.
"We always felt 140-145 would be a good total. We had three quality spinners and the quality in bowling to contain them," said Gambhir after his side's 32-run win over the hosts that has virtually assured the Knight Riders a place in the play-offs.
"The way Shakib and Abdulla bowled was fantastic. The way Shakib bowled the first two overs out of the first six set up the game for us," he added.
Gambhir said the team can be a bit more relaxed now going into the final round robin match against the struggling Pune Warriors on May 19 at the latter's territory -- the Subroto Roy Sahara Stadium.
Stating that the Knight Riders' aim is to finish in the top two in the league table, Gambhir said, "It was a fine win, but we have a long way to go. It was a must-win game for us. "Hopefully we can be a little relaxed, try to express ourselves more in the next game and finish among the top two, which gives us two cracks in the play-offs, which is very important. "Last time we had one bad day in the play-off and were out of the tournament. Hopefully we can win the next game and finish in the top two which gives us two opportunities."
The loser of the first play-off between the two top finishers at the end of the league stage gets a second chance to enter the final through another game against the winners of the second play-off game between the third and fourth-placed teams in the table.
Heaping praise on Manoj Tiwary for his crucial knock of 41 that rescued Kolkata from a difficult 6 for 2, Gambhir said in the context of the team's final total it was a huge effort.
"When you have lost two early wickets, partnership was important. One batsman had to bat through. That 41 out of 140 (made by Manoj Tiwary) was crucial. The way Manoj batted he can take a lot of confidence into the next game."
The captain also praised the bowling efforts of West Indian off spinner Narine, the team's new recruit for the season, but added that the whole bowling unit of the Knight Riders had done a tremendous job in the tournament.
"I don't want to talk about individuals. He's been doing a fantastic job for us. But it's not only about Sunil Narine but is about other people as well. The entire bowling department has done a fantastic job for us. Most of the matches we have been able to contain the teams to 130-135. "
"Sunil is one of the most successful bowlers but you need other four or five bowlers to complement him as well. All the other guys have done a fantastic job. Credit goes to the entire bowling department. We are very lucky to have him in the side," said Gambhir.
India opener also sprang to the defence of the under-performing Yusuf Pathan and said he was a potential match-winner who will come good very soon.
"He has been striking the ball well. In the last game against Mumbai (in Kolkata) he was striking the ball well. We have faith in Yusuf. He will do something magical very soon and may be when it's required the most he will come good. "He's a potential match-winner and would come good. It's just a matter of time he will do something magical. He has done magical things in the past. There's no point in giving him rest, it's about giving him more confidence. Very soon he's going to do something good for us, I feel."