But there is no place for the experienced scrum half Mike Phillips. His nagging knee injury has forced hi to sit out the Melbourne Test.
"This is a do or die match for Australia and it's going to be a real battle out there. We've decided to add a little bit more physicality to our side up front," said Gatland.
"Dan Lydiate brings that and then we have the explosiveness of Tom Croft and Sean O'Brien to come off the bench. We are really happy with the quality we have on the bench.
"Mike Phillips was fit and available, but he has had problems with his knee. It has been sore and he hasn't been able to take a full part in training. The decision was to rest him for this week and he is potentially an important component for next week.
"We wanted to make sure, given the quality of the No 9s we've got, all of whom have done a great job, he is 100 per cent fit for next week by giving him a few days off."
The Lions are chasing a win at the Etihad Stadium this weekend that would earn them their first Test series victory since 1997. They went 1-0 up in the last series in Australia 12 years ago, but then lost the last two Tests.
"One or two changes were forced on us, and we've got a couple of players coming back from injury, but it just shows how strong the squad is and that we have a huge amount of competition," added Gatland.
"I don't know who made that thing up about not changing a winning side - it is about picking the best team to do a job for us. We can win this series by winning on Saturday and that's where our whole focus needs to be.
"The last thing we want to think about is being one-all and having to play another game in Sydney. Everything for us is about Saturday night."
The Lions crept over the winning line last week in Brisbane, 23-21, but could so easily have lost to the last kick of the game. This weekend the Wallabies will have their top choice goalkicker in action in Christian Leali'ifano.
"Christian has been playing well for the Brumbies. Just like us they will have a number two and three kickers lined up just in case of injury and I am that James O'Connor and Kurtley Beale will have been doing plenty of kicking practice this week.
"It was tough for him last week getting knocked out in his first Test match after 30 seconds, but he has come through all the protocols for concussion and they wouldn't have taken a risk on him unless he was passed 100 per cent fit.
"World Cups have been decided on the quality of goalkicking and it was one area we decided that needed a huge amount of attention and Neil and the kickers have worked really hard at it.
"Leigh Halfpenny is just a brilliant individual. If you look at him prepare in training and the way he strikes the ball. Even if he misses it is only by a foot to the left or the right and he is able to compensate for that.
"Credit needs to go to Neil Jenkins for the work he has done with all the kickers. You saw the accuracy of Owen Farrell on Tuesday night and the confidence he has got. Stuart Hogg is coming on really well as well. The goalkicking has been excellent."
Gatland had a meeting with South African referee Craig Joubert earlier in the week to clear up a few technical aspects about the breakdown and he knows that if the Lions are to make it 2-0 they have to concede fewer penalties than they did in Brisbane.
"We've had a good meeting with Craig Joubert and we've got some clarity on the break down, which was good. The scrum started well, but we've got to ensure that we are accurate for the full 80 minutes.
"We gave away one or two too many penalties last week, so our discipline needs to be really strong as well."