Gautam Gambhir claimed hitting a six to bring up his century Wednesday was the safest shot he could have played then.

Gambhir hit an unbeaten 149, having brought up his hundred by thumping medium pacer Shane Watson for a six over mid-on as the hosts finished the first day of the third Test at a commanding 296 for three.

It was Gambhir's third career Test century and second against Australia, the earlier one coming in the second Test at Mohali.

"It was the only option I had because there were fielders all around me to save the single," Gambhir said.

"I thought the best thing was to go over the top. It was an instinctive shot and the safer option rather than trying to tuck the ball and attempting a single."

Gambhir said he was determined to get runs against Australia, especially after failing against them on his debut in Mumbai in 2004.

Handed the opener's role, the left-hander made just three and one in that match.

"I had a dream to score runs against Australia and perhaps the dream is coming true," he said.

"I still remember my debut Test match - it wasn't anything to remember and I was determined to make runs in this series.

"It was a big motivation for me coming into this series and so far it has been working for me."

Gambhir will treasure both his centuries, but believes this one could turn out to be more important.

"Both are very different centuries," he said.

"In Mohali, we were 200 runs ahead and we had the freedom of playing our natural game.

"Here it was the first innings of a Test match and it's really important to set the tone for the entire five days.

"Prior to Mohali I was under a lot of pressure as I was getting starts, but was unable to convert them.

"I always believed that a hundred was just around the corner and if I got one it would be the turning point.

"Perhaps I am a lot more relaxed now, having got that hundred at Mohali."

Gambhir claimed his slow run-rate in the morning was due to the circumstances.

"We had lost two quick wickets and it was important for someone to continue and get big runs.

"It is never easy playing against a competitive side like Australia. They do not give away easy runs.

"Brett Lee and Stuart Clark were on target in the morning and in Test cricket you have the opportunity to see out a good spell of bowling and capitalise later on.

"That's exactly what happened today."

Gambhir's hundred has helped put India in a strong position, and the 27-year-old reckons Australia will find it hard to make their way back into the match.

"We've got two quality spinners in our side and the way (Amit) Mishra bowled in the last match, it's not going to be easy for the Australians.

"If we bat well tomorrow Australia will be under a lot of pressure.

"It's not going to be easy at all especially if you look at the amount of turn which Simon Katich was getting. This is the first day mind you.

"The ball always turns at the Feroz Shah Kotla from the third day so it's going to be hard work for the Australians.

"The bounce is also inconsistent on the third, fourth and fifth days when the wicket starts breaking.

"Given the quality of our seamers, Australia will find it difficult."

Gambhir exchanged words with Simon Katich and Watson on Wednesday and, in an incident just after tea, nudged Watson with his elbow while completing a single.

Gambhir played down the clash, saying: "It's part of the game.

"They were really desperate to get me out and they were trying to get me to lose concentration.

"I didn't do it deliberately."