NOOSA HEADS, Australia (AP) — Jamie Roberts has no illusions about the task at hand after replacing Brian O'Driscoll in the British and Irish Lions for the third and deciding rugby test against Australia.

"A thousand people have said it before me, and thousands will say it again," Roberts told a news conference Wednesday. "He is one of the greatest players to have played this game."

But O'Driscoll was not named in the 23-man lineup by coach Warren Gatland for the Sydney test as the visitors attempt to win their first series since 1997.

Roberts was among those shocked that O'Driscoll, touted as possible captain due to the injury absence of Sam Warburton, wasn't in the lineup.

"Surprised is not the right word," Roberts said. "Warren has made some big calls and ultimately you respect the coach's decision. He's picked the team that he feels will win Saturday, whether that includes Brian O'Driscoll or not.

"A lot of very, very good players missed out on playing Saturday. It shows you how competitive the environment is."

Roberts was thankful that a hamstring injury sustained in a tour match against the New South Wales Waratahs on June 15 didn't end his tour.

"It's been very tough," the Welshman said. "First and foremost thanks for the medical team for getting me here. I thought I'd be on my way home. I had a scan, and they said we're going to keep you on tour, we're going to keep faith in you. Now it's great to be playing a part in the big day Saturday."

Roberts said O'Driscoll was a class act in reaction to his omission from the test squad.

"It was the most nerve-wracking team selection I have ever had in my career," Roberts said. "To show what kind of guy he was, he (O'Driscoll) was the first guy to come up to me after training today and say 'do you want to do any extras?'"

In 2009, when the Lions lost the deciding match to South Africa, Roberts wasn't in the lineup.

"I had injured my wrist in the second test and couldn't play in the third one," Roberts said. "So to play in the deciding test, probably that and a World Cup final is the ultimate, it's a great stage."

Roberts adds some extra size to the Lions backline, joining Welsh teammate Jonathan Davies in the midfield, and with the big, physical Mike Phillips returning at scrumhalf.

"There are going to be some brutal collisions," Roberts said. "It's a game of inches. You play on the front foot and you can look a million dollars. You play on the back foot, you can look very average. "