It keeps the defending champions at the top of the Aviva Premiership table and continues their fine recent form. They scored three tries through Tom Williams, Nick Easter and Charlie Matthews and O'Shea believes it was a vital victory.
"I'm incredibly happy," he said. "We felt coming up here that it was going to be an incredibly tough match. We knew they would fight tooth and nail for everything and anything they could get their hands on."
He added: "Credit to our guys. To come here and get a win like that is huge for us, especially with the number of players we had missing (because of the RBS 6 Nations). These are the games that people don't remember in May but they're massively important."
O'Shea also praised scrum-half Karl Dickson who took advantage of Danny Care's England call-up to put in an outstanding display.
He added: "Dicko was chomping at the bit. He's such a competitive player, that's why he travelled with England as 24th man to France last year and he went to South Africa. We're very, very fortunate to have two scrum-halves of that ability."
Despite a controversial performance by referee Martin Fox, Sharks director of rugby Steve Diamond refused to be drawn on the display.
Diamond twice spoke with the referee's assessor in the first half but wryly said in his post-match press conference: "It was probably the best refereeing performance I've seen all year. (I'm saying it) with an absolute straight face that it was the best refereeing performance I've seen since I've been back coaching."
Sale also crossed the whitewash three times through Cameron Shepherd, Richie Vernon and Sam Tuitupou, but it was not enough to take them off the bottom of the table.
Diamond added: "Harlequins disrupted the game plan, they are fantastic at what they do so we've got no qualms and we were beaten by the better side."
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