Manchester United manager Louis van Gaal described his team's display as "not good" despite a 3-2 win over Roma in the United States.
Wayne Rooney struck twice and created a goal for Juan Mata as United hit three first-half goals in Denver.
But Van Gaal suggested his best passers were off-form - picking out Mata, Ander Herrera and Shinji Kagawa.
"I am pleased that we have won but it was not a good performance," the Dutchman said.
"54,000 people came to watch us but we can perform much better.
"All my good passers failed today. I think it was because of the height and the air.
"Mata, Herrera and Kagawa - these are the best passers (at the club), and everything went wrong."
|Man Utd line-up v Roma|
|Johnstone (Amos 46); Jones (M. Keane 46), Evans (Smalling 46), Blackett; Valencia (Young 46), Cleverley (Hernandez 70), Herrera (Kagawa 46), James (Shaw 46); Welbeck (W Keane 46), Mata (Lingard 46), Rooney (Nani 46). Subs not used: De Gea, Lindegaard, Fletcher, Zaha.|
Rooney's 36th-minute opener from 20 yards sparked a three-goal flurry at the end of the first half.
Mata lobbed home after a raking pass from England striker Rooney, who then scored a stoppage-time penalty.
Miralem Pjanic netted an amazing 75th-minute strike from inside his own half for Roma, before Francesco Totti's 89th-minute spot-kick.
"In the second half we forgot to keep the ball," Van Gaal said. "When you are 3-0 ahead, the only thing you have to do is keep the ball in possession and the opponent has to run and run and run.
"We forgot to do that. We brought Roma back into the match."
Victory was United's second in succession under Van Gaal, following a 7-0 defeat of LA Galaxy.
Roma started the brighter, with Mattia Destro breaking clear in the second minute and lifting a shot over Sam Johnstone - but the ball bounced narrowly over the crossbar.
Mostly, though, it was a series of misplaced passes, poor control and general lethargy in the 30 degree heat.
Rooney lifted the torpor, curling home in exactly the same manner as he had been practising at the other end of the pitch in Friday's training session.
He then created United's second with an arrowed pass from inside his own half. Mata's one-touch control was instant and his delicate finish perfect
United were on a roll and when Danny Welbeck was prevented from reaching Herrera's return pass by Mehdi Benatia, Rooney's powerful penalty sent Lukasz Skorupski the wrong way from the spot.
As promised, Van Gaal made nine changes at the break.
His preferred system of three central defenders meant an unaccustomed right wing-back role for substitute Ashley Young - and he was soon booked for sliding into Leandro Castan.
In a game of excellent goals, Pjanic scored the most spectacular, lobbing Ben Amos from 60 yards.
Totti then converted a penalty following Michael Keane's handball a minute from time, but United held on and face Inter Milan next in Washington on 29 July.