The wing-back enjoyed plenty of space down the flank as Sergej Jakirović's newly promoted side outwitted Michael Carrick's United using just three matches of preparation, bullying the visitors from start to finish despite carrying eight pre-existing injuries into the game and losing both goalscorers, Semi Ajayi and Nobel Mendy, during the match itself.
Giles, asked about keeping a clean sheet and dominating from start to finish, did not hold back.
"We did a number on them. It doesn't get much better than that to be honest. To a man everyone was great and the stadium was rocking. It is something to take confidence from.
"We knew what they were about and we've done what we needed to do. We take confidence from it."
Hull City have been tipped for relegation this season, much as they were last year in the Championship when the club operated under two separate transfer embargoes, and Giles said the players had taken note of pundits writing them off before a ball was kicked.
"We've seen it and we need to use it as fuel. I appreciate that everybody might feel like we might go down, but we shouldn't get too caught up in it. Days like today can send a statement out. I do believe we can cause teams more problems this season.
"I'm hoping days like today send a bit of a message to the rest of the league and everyone watching that we're not just here to make the numbers up. We know it's going to be tough but there's a good core in that dressing room, with brilliant togetherness and resilience and if we could stick to that we can go toe-to-toe with a lot of teams this year."
Asked whether he had been surprised by how poor Manchester United looked, Giles pointed to a clear gameplan.
"Not really, we knew set-pieces are massive in this league. We've got legs to burn on the counter-attack. We've got big Oli Mac in the box."
Jakirović had built his approach around exploiting United's pre-season vulnerabilities, targeting the flanks with quick switches of play to set up physical battles for striker Oli McBurnie against 19-year-old defender Ayden Heaven, a plan that paid off as McBurnie's performance underlined a glaring gap in United's own attacking options.
United captain Bruno Fernandes admitted afterwards that the team had failed to prepare for Hull's aggressive, high-energy approach, while Carrick opted against using summer signing Joshua Zirkzee altogether. Benjamin Sesko featured for the first time since April but remains short of full sharpness, and Marcus Rashford was introduced at half-time for his first competitive United appearance in 20 months.
The defeat leaves United with an unwanted piece of history, following their penalty shootout loss to a fourth-tier side in last season's League Cup with a chastening result against a newly promoted side missing several first-choice players.
Eight of the players who led Hull to play-off victory over Middlesbrough at Wembley returned to the starting line-up, with goalkeeper Konstantinos Tzolakis and Mendy both making standout Premier League debuts. Hull spent just £70 million on 12 players this summer, a fraction of what United are set to pay Brighton for Carlos Baleba alone.