John Kingston paid tribute to his makeshift team after they stunned Aviva Premiership Rugby champions Saracens with a great performance at the Stoop.
Charlie Walker and James Chisholm were both late inclusions due to injury, while Mark Lambert entered the fray within a minute after Joe Marler was injured.
And with Saracens battling back, Karl Dickson provided a steady hand when he came on for Danny Care to see out the 17-10 win.
“Joe’s a massive personality for us. Mark Lambert has been at the club a long time and he took the role seamlessly so early in the game,” Kingston said.
“Karl Dickson came on when Danny had to go off after half-time when we were massively under the pump and playing into the wind. He did such a wonderful job.
“Charlie Walker didn’t get much notice that he was playing after Marland (Yarde) pulled out before the match.
“And then James Chisholm stepped in for Jack Clifford, who had that unfortunate injury.
“The way they all played when there was so much disruption was really positive. You expect your big players to play, but those boys stepped in and a wonderful job.
“It must have been a wonderful game to watch, two sides going at it hammer and tongs.
“I’m just so pleased for the players that they got their rewards and an injection in belief and confidence which was very important for the season ahead.”
Early scores from Tim Visser and Walker helped Quins into a 17-0 lead and despite some huge pressure from the visitors, they held that lead through to half-time.
Richard Wigglesworth crossed early in the second, but some errant kicking and rock-solid defence ensured they had to settle for a losing bonus point.
And director of rugby Mark McCall admitted they had given themselves too much to do.
“A 17-0 lead is a big lead to take into half-time. It was an uphill battle in the second half,” he said.
“Overall we have to be disappointed with our performance. It was 10-0 but nothing had really happened in the game.
“They then scored again quickly and your mind starts playing tricks on you, you think they’re more on top of you than they actually were.
“I don’t think they go into our 22 again for the rest of the game and we seemed to spend a lot of time down their end. But Quins played well.”
Harlequins: Brown, Walker (Alofa 51), Hopper (Jackson 68), Roberts, Visser, Swiel, Care (Dickson 48), Marler (Lambert 1), Buchanan (Gray 48), Collier (Sinckler 48), Merrick (Twomey 68), Horwill, Robshaw, Wallace, Chisholm
Not used: Ward
Saracens: Goode; Ellery, Bosch (Tompkins 64), Barritt, Wyles; Lozowski, Wigglesworth (Spencer 66); M Vunipola (Barrington 66), Brits (George 41), Du Plessis (Figallo 41), Itoje, Hamilton, Rhodes (Brown 59), Wray, B Vunipola
Not used: Gallagher, Spurling
Tries: Visser, Walker
Conversions: Swiel 2
Referee: Craig Maxwell-Keys