Gatland said he was determined not to allow "sentiment" to affect the Lions' chances of winning the series and has rejected the suggestion his chosen XV contains too many Welshmen, with 10 in the starting lineup.
O'Driscoll had been heavily tipped to take over as captain for the deciding Test in Sydney following Sam Warburton's hamstring injury. Yet Alun Wyn Jones will instead lead a side that features seven changes, one positional, from the one that lost last weekend. The team announcement inevitably generated a firestorm of comment, with critics labelling the decision to drop the 133-cap Ireland centre O'Driscoll "a terrible mistake" that could cost the Lions victory.
The 1974 Lions captain, Willie John McBride, said: "I was absolutely gutted. The first thing that came into my mind was that Robbie Deans, the Australia coach, must be laughing all the way. The Australian media have convinced him to drop O'Driscoll, which I find amazing, I must say. He was the guy I would have picked as captain of the tour. He has been a big influence on the tour but you live and die by the team you pick so we will see what Saturday brings."
The former Australia wing David Campese claimed the Lions had just "handed the series to Australia", adding: "Obviously the changes have occurred because Gatland's panicked a bit." The former Ireland captain Keith Wood said: "Brian O'Driscoll has been quiet in the two Tests but at every stage, he has been the clarion call once Paul O'Connell got injured. I just think Gatland has made a terrible mistake."
A host of current players, including the All Blacks fly-half Dan Carter and the Toulon centre Matt Giteau also took to Twitter to question the wisdom of O'Driscoll's omission.
The 34-year-old Irish centre has not even been picked on the replacements' bench – Gatland has opted instead for a midfield pairing of Jamie Roberts and Jonathan Davies, with Manu Tuilagi on the bench – bringing to an abrupt close an illustrious Lions Test career spanning four tours.
Gatland, however, stressed the choice was made purely on rugby grounds and is less concerned about romantic happy endings than securing a first Lions series victory since 1997. He even hinted it had been a relatively straightforward decision following an hour-long selection meeting.
"It's only hard because you are making the decision using your head and not your heart. Then you realise that what comes of making a decision like that is all the peripheral stuff, because it becomes a major story for 48 hours and it becomes a debate.
"I'll go back to the UK after this and say: 'Did I make the decision because I believe it's the right decision or did I make it because it was politically right?' I have to put hand on my heart and say it's the right rugby decision. I would hate to think we had made calls to avoid criticism or for reasons of public popularity."
None of this will soften the blow for O'Driscoll, never previously dropped in a 14-year career in which he has won 133 Test caps and led Ireland to 52 wins in 83 matches. He also captained the Lions in New Zealand in 2005, only to be ruled out of the series after being injured in the early moments of the first Test in Christchurch, and is only the third player in 125 years to embark on four or more Lions tours.
In the twilight of his playing days he was desperate to help steer the Lions to success in Australia and Gatland admits the news did not go down well. "He is obviously very, very disappointed, as any player would be. It's kind of hard when you've been the number one in your position for so long and first choice on every team you've been a part of."
Gatland, nevertheless, is standing by his decision to award the captaincy to Jones. "I don't know why people are trying to make an issue out of that. I don't see it as an issue at all. Alun Wyn Jones has captained his club side a lot, he has captained Wales in the past. We went and picked what we thought was the best team we think can take the field and do the job. After that it was who do we think can captain the side?"
Jones, who received a much-publicised boot to his face early in the first Test which required the Wallabies captain James Horwill to attend two disciplinary hearings before being cleared, said O'Driscoll had been "very professional" in his response to the news. "He just congratulated me, simple as that. Nothing more has been said. He just got on with the job in training this morning. Everyone has done the same. We haven't got a lot of time to waste now. We've got three days that are going to set the tone in the final Test, three days which are hopefully going to give us a Test series win."
Gatland has been impressed with Davies's form on this tour and with Roberts having recovered from hamstring trouble, has reunited the all-Welsh combination which helped win a Six Nations grand slam last season and retained the title this year. "I thought Jonathan's performance against New South Wales was probably one of the best displays I've seen from him.
"Our kicking game was poor last week. We wanted to put the ball behind them a little bit which we didn't do well enough and Jonathan is a left-foot kicking option for us. He didn't get a lot of ball to go forward last week but when he did carry he made a couple of good dents in them."
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