United hardly came racing out of the traps and were caught out after a period of the two teams sizing each other up.
A quick free-kick led to Davide Zappacosta trundling down the right flank, with no defender picking up his run or Pasalic in the middle. It was hardly the speediest attack in the world and yet the midfielder was all alone to stab home from three yards out.
Something of a response came, Fred firing straight at Juan Musso from the best opening, before Atalanta doubled their lead with Demiral’s powerful header when left untouched at a corner.
Fred, again the wrong man in the right place, danced through to fire wide moments after Demiral had expertly cleaned out Marcus Rashford after he was set free one-on-one. The returning striker lashed over from an even better position before the break and United were booed off.
The excellent Demiral was forced off at half-time and an Atalanta defence shorn of multiple starters threatened to creak when Ronaldo ran clear in the early seconds, only to fire straight into Musso.
The warning signs told and Fernandes picked out Rashford with a perfect through ball, allowing the England attacker to take aim and cooly roll home to ignite Old Trafford with his second goal in as many games.
Atalanta edged their way back into the game and forced David De Gea into a smart double save before Maguire levelled the score. The defender hovered at the far-post for a cross that drifted through a crowd, and was finished with aplomb.
Musso threw a fresh right hand out to block Fernandes’ attempt but could not do anything about the playmaker’s Portuguese colleague.
The scene was a familiar one in front of the Stretford End. A cross from the left, a mesmerising leap, and a perfect header bulleted into the opposite corner – to mark his 300th appearance for the club in style.