Aston Villa began their Premier League season with a win, but it came against 10 men following a red card shown to Republic of Ireland defender John Egan.
The Sheffield United centre-half was involved in a tussle with striker Ollie Watkins, who was chasing a long ball from Tyrone Mings in the 12th minute.
Graham Scott opted to brandish Egan a straight red card, even with Aaron Ramsdale coming to clear the ball.
Eleven minutes before the break, United were awarded a penalty when Chris Basham was tripped by Matt Targett. John Lundstram stepped up to take the penalty, but it was saved by Villa debutant Emiliano Martinez.
Villa eventually broke the deadlock midway through the second half. A Conor Hourihane corner was flicked on at the near post by Tyrone Mings to be met by Ezri Konsa who nodded past Ramsdale.
Watkins and Trezegeut were among those to miss second-half chances for Villa, who held on for all three-points despite a spirited United display.
Defeat means Chris Wilder has lost three games in a row in charge of the Blades for the first time in his tenure.
The win completed a fine day for Villa, who saw Tyrone Mings sign a new deal keeping him at the club until the summer of 2024.
The 27-year old only signed a permanent deal last year following a season on loan from Bournemouth. He's made 38 appearances since and earned an England call-up.