Saracens edged a gripping derby by pouncing late to defeat Harlequins 29-22 but an important Gallagher Premiership victory was marred when Billy Vunipola sustained a knee injury.
Vunipola limped off late on at Twickenham Stoop with a medial collateral ligament problem and the extent of the damage to the out-of-favour England number eight will be known this week.
"We don't know how serious it is, MCLs can range from not too bad to serious," director of rugby Mark McCall said.
Jackson Wray's late try enabled by a defence shredding run from Alex Lewington completed Saracens' fightback after they trailed 19-9, but it was the place kicking of Alex Lozowski that really kept them in the chase.
"We weren't ourselves in the first half. We were three tries to nil down and they had their tails up. We rolled up our sleeves and fought together," McCall said.
"Alex's kicking was unbelievable if you look at where his place kicks have come from - either from halfway or on the touchline pretty much.
"That is crucial in games like that. Even his conversion at the end to make it a seven-point game instead of a five-point game.
"All our senior players led the way – Billy, Mako Vunipola and Alex Goode, who nearly didn't play because he was ill."
McCall was keen to praise Alex Lozowski who was the player of the match after a flawless kicking display in south-west London as they ended their rivals unbeaten run at home.
“He’s been amazing. He started well against Bristol and was 100% from the tee that day as well. They were difficult kicks but he’s played really well for us so far this season.”
Harlequins senior coach Tabai Matson admired the determination that enabled Saracens to pinch a win that lifts them to second in the table.
"We knew we had to be at our best to get a result. One of the things you respect about Saracens is they never lose a game, you have to beat them," Matson said.
"You have to take a game off them and we weren't able to do that. It's disappointing."
Saracens will look to continue their impressive start to the season when they host London Irish on Saturday.
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