Hill led from the front in his first match after six months out injured and grabbed a try in a stirring second-half fight-back for Saracens.
Ben Russell also touched down for the men in black while Thomas Castaignede added 16 points with the boot.
A delighted Graham said: "Overall it was an outstanding team performance.
"There were some fantastic individual performances from some of the young guys and they have really given us something to think about for selection next week.
"It was great to see Hilly back and Paul Gustard leading the team. Thomas Castaignede showed his usual full box of tricks and had a 100% kicking record.
"Tom Mercey acquitted himself well against an international prop in Tim Payne and got even stronger as the game wore on.
"The boys responded superbly after last weekend (a 20-17 defeat to Worcester) and they proved that tonight with a very committed performance in the second half.
"We controlled the ball a lot better in the second half and it was a much better display."
Wasps led 10-6 at half-time through tries by Tom Voyce and Joe Ward but were blown away by the home side's second-half performance although Voyce added a third try late on."
And Wasps' director of rugby Ian McGeechan promised his team would be back to full strength for next week's Heineken Cup clash against Benetton Treviso.
He said: "Overall I'm pretty pleased. We got some good tries in some horrendous conditions.
"In rugby terms I was pleased with the youngsters. They were not intimidated at all.
"I thought they were good on the ball and they manufactured all three tries so in that respect it is very encouraging.
"Everybody will be back next week. I gave a lot of lads a week off after the internationals because we do try and take care of them.
"It's good to see Hill back. He is a great player and it's good to see him make a full recovery when he had such a bad injury."
Cardiff Blues coach Dai Young celebrated a hat-trick of English "scalps" with his side's 31-7 defeat of London Irish.
The Welsh side topped their group and secured passage to the semi-finals of the EDF Energy Cup with a fine performance against the Guinness Premiership side.
"We've had three big wins against English opposition, three big scalps, and it shows how much we're progressing," said Young.
"We haven't won anything, but we're in the last four. That's the sort of thing that's been beyond us in the last couple of seasons."
Young had particular praise for man of the match Martyn Williams, back from Welsh international duty to score the opening try.
"He's never played a bad match for us," said Young.
"Some games he's brilliant, some games he's just very good. Tonight he was up there with the best.
"It was tremendous, considering he'd just come back from playing the All Blacks."
London Irish head of rugby Brian Smith was disappointed with their set-piece play, but accepted his team selection had played a part.
"I was a bit cheeky in that I made a lot of changes from our normal line-up and they didn't really work for us.
"But I don't want to take anything away from the Blues. They're a quality team.
"To score that many tries in these conditions was a fine performance."