United were able to welcome back 10,000 fans for last season's home finale against Fulham, and there was around triple that figure in attendance for Brentford's preseason visit as both sides got more valuable minutes before the start of the new Premier League campaign.
Preseason games can often be forgettable, but those present witnessed one of the great Old Trafford goals as Pereira hit a 25-yard rocket that went in off the underside of the bar in front of the Stretford End.
The long-term future of the United academy graduate, who spent last season on loan at Lazio, is unclear but nobody will forget his strike against Thomas Frank's men - a goal reminiscent of Tony Yeboah's stunner for Leeds against Liverpool in 1995.
It was a match of great goals, started by promising 19-year-old Anthony Elanga producing an excellent volleyed finish from an Aaron Wan-Bissaka cross in the 12th minute.
Brentford produced a moment of magic of their own eight minutes later when Shandon Baptiste hit a swerving volleyed effort from the edge of the box that went in off the woodwork.
Pereira's stunning goal early in the second half was the pick of the bunch, but it did not prove the winner as substitute Bryan Mbeumo curled home smartly after half-time introduction Diogo Dalot failed to intercept a ball down the line.
Additional reporting by PA.