LONDON (Reuters) - Steve Johnson says he will draw inspiration from doubles partner Sam Querrey as he attempts to pull off a second huge upset at this year's Wimbledon, against Roger Federer on Monday.

Querrey sent shockwaves around the sporting world when he broke Novak Djokovic's stranglehold on the game by knocking the world number one out in the third round on Saturday.

Unseeded Johnson, in the fourth round of a grand slam for the first time after beating Grigor Dimitrov, said Querrey's exploits were a shot in the arm for the underdogs.

"Gives everybody confidence. You see Novak lose, you sense the locker room, like believe there is a chance," the 26-year-old told reporters.

"(Djokovic) has that aura about him right now, as did Roger back in the day and as did Rafa at the French.

"Once you see him go down, I think guys will start to believe that they also can do it. So I think it's going to be interesting."

Johnson said fellow Californian Querrey's positivity was infectious.

"Hopefully, you know, his good vibes -- he's a very happy-go-lucky guy -- hopefully his positivity out there wears off on me as well and I think vice versa."

Johnson has never played Federer but believes he can upset the seven-times Wimbledon champion who is yet to drop a set.

"It's going to be a great experience. I'm going to go out there thinking I'm going to be the winner," he said.

"I have no fear out there. I'm going to go out there and try and play my best tennis and hopefully my plan works."

Johnson might even copy Querrey's pre-match preparation, after revealing that the 28-year-old relaxed during the rain breaks that interrupted his match against Djokovic by practicing his putting in the locker room.

"Sam is Sam. He's in the locker room joking, golfing around, putting. Man, you have Djokovic two sets on the ropes.

"There are a bunch of putters in there. He was putting around. Having fun with all the guys in the locker room.

"But for him it works. It's great. Sam's a great guy."

Querrey takes on Frenchman Nicolas Mahut on Monday.

(Reporting by Martyn Herman, editing by Ed Osmond)