Close-season signing Fraser McKenzie opened his scoring account as Sale handed Wasps their first Premiership defeat of the season.
The 23-year-old former Scotland Under-19 captain - signed from Edinburgh - sparked a fine recovery by the Sharks, who dominated for long spells to turn the match around after trailing 10-3 after 14 minutes.
Sale's other try came from skipper David Seymour with 19 points from the boot of fly-half Nick Macleod, relishing the role of front-line kicker following Charlie Hodgson's move to Saracens.
Macleod took his points tally for the campaign to 41 from three matches with five penalties and two conversions as Sale notched their second victory of the campaign.
Former Sale centre Chris Bell and fly-half Ryan Davis scored the Wasps tries, with Davis adding a conversion and two penalties.
Diamond said: "Nine or 10 of our squad were 21 or under. We've 19 and 20-year-old props who are learning by the week.
"The scrum was very good today and we got the penalties we deserved."
He revealed Wales scrum-half Dwayne Peel's withdrawal early in the second half was precautionary.
"Hopefully he'll be all right for next week," said Diamond, who added: "Peel and Nick Macleod at half-back controlled it for us.
"The young props (Lee Imiolek and Henry Thomas) did well, Marc Jones put some solidity into the pack and Kearnan Myall was the man of the match for me. He controlled the lineout."
Wasps rugby director Dai Young was disappointed by his side, who had won their opening two Premiership matches.
"It was a poor performance," he said. "We started well but after that you have to say we came second best in everything really.
"It was disappointing from the last two performances but we lacked real accuracy and real energy as well.
"You just put your hands up and say they were a far better team and deserved it."
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