Worcester looked down and out just two months ago, but successive home league wins against Bath, Newcastle and Saracens kept them afloat.
And Sanderson, who could lead an under-strength England squad in South Africa this summer, typified a colossal Warriors effort.
Brain said: "We were ice-cool under pressure, and all credit to the players. We had a plan, and the players really executed it.
"I am delighted for all the supporters and for (chairman) Cecil Duckworth. If we play like that every week, then we won't have an issue with relegation.
"We talked about attacking Saracens as an eight. Craig Gillies coming back after suspension was key, and I thought Aleki Lutui and Pat Sanderson were outstanding.
"Pat led the team extremely well. He said all the right things in the build-up to the game, and he definitely did the business under pressure today."
Worcester played as though they were devoid of any relegation fears, and Brain confirmed a relaxed mood in the camp.
He added: "It was all about tying to do the right thing at the right time. We trained well all week, and the players watched a movie yesterday to the theme tune of The Great Escape.
"But you cannot get by on passion in this league, you have to execute things."
Worcester have already secured the services of All Blacks centre Sam Tuitupou next term, while Brain has not ruled out retaining England's 2003 World Cup defence coach Phil Larder, who has worked in an advisory capacity at Sixways this season.
Brain said: "Phil Larder is in Spain at the moment. I spoke to him on the phone a couple of times during the game, and he's had a very good input with us.
"I would like Phil to remain as part of the coaching staff."
Despite losing, Saracens secured a fourth-place finish and play-off trip to Gloucester next Saturday.
Saracens rugby director Alan Gaffney said: "Our goal was a top-six finish, but our dream goal was top four. We are euphoric about achieving that, although you can't be euphoric about the performance today.
"Worcester played with a lot of pride, passion and skill. We have got to take it on the chin, and each of the players and coaches must look at their own performances.
"It is very difficult to see how Worcester finished where they did in the league. Their defence was aggressive, and they had a lot to play for, but so did we.
"We are competing with the elite at this level now, and we always wanted to do that. We've got nothing to hide from Gloucester next Saturday.
"I don't think anyone would have suggested we would make the top four this season - someone even suggested we would be relegated - so we are very happy, but we have got to try to move forward into next week.
"We got bashed today. We still tried to play rugby, even though our set-piece was under a bit of pressure, but we think we can compete down at Gloucester."
Gaffney, meanwhile, played down any injury fears surrounding England World Cup-winning flanker Richard Hill, who withdrew from the game just before kick-off.
He added: "Just prior to the warm-up, Richard tightened up in the knee. He could have played, but there was no point risking him. He is okay.