A week that started with an ill-tempered FA Cup quarter-final defeat at Chelsea - and unnecessarily arduous journey home from London - continued with what was expected to be a straightforward home clash against the unfancied Russians.

Rostov were on the back foot from the outset but were beginning to give United the jitters before Mata ended a move he started, securing a 1-0 second-leg win that sees Mourinho's men through the last-16 tie 2-1 on aggregate.

Last week United had just been pleased to make the long trip back from Russia with an away goal and without any injuries given the dreadful state of the Olimp-2 pitch.

The superb Old Trafford surface was always going to make the return leg a different prospect and so it proved in a dominant first half, with Zlatan Ibrahimovic twice hitting the woodwork as United got away 12 attempts and enjoyed 76 per cent possession.

However, it took until the 70th minute for Mata to settle growing nerves, turning home from close range having started the move just inside his own half.

There was still time for a few scares but back-up goalkeeper Sergio Romero saved United's blushes, denying substitute Aleksandr Bukharov's header before an exceptional stoppage-time save from Rostov captain Christian Noboa's free-kick.

United will be relieved to be in the quarter-final draw and hoping for good news regarding Paul Pogba and Daley Blind after both limped off in the second half.

Few could have foreseen such a nervy ending given the way Mourinho's men flew out of the blocks.

Starry-eyed Rostov goalkeeper as Nikita Medvedev unconvincingly stopped Marcos Rojo's early header, breathing a sigh of relief as Ibrahimovic sent the ball against the post.

Rostov's goalkeeper looked more assured after recovering from being rounded to get a hand on an Ibrahimovic effort as United continued to try and prise open the visitors.

The Old Trafford faithful were as perplexed as Henrikh Mkhitaryan after officials ignored goalkeeper Medvedev's inexplicable push on him in the box - frustration that was inches away from being forgotten.

Mata sent Mkhitaryan through with a cushioned half volley, but last week's goalscorer clipped just wide as United pushed for a first-half breakthrough.

Ibrahimovic again came close to adding to his 26-goal haul, cutting in superbly to hit a fierce right-footed strike that rattled the post.

Only a fine Medvedev stop prevented Pogba capping a solid display with a goal in first-half stoppage time - his last contribution of note as he pulled up 45 seconds after the restart.

The France midfielder looked to win his race with Denis Terentyev, only to sustain an apparent hamstring injury that led to Marouane Fellaini's introduction.

It was a frustrating start to the second half and nearly worsened.

One-way traffic meant Romero did not have a shot to face until the 54th minute, when highly-rated Sardar Azmoun wriggled free to get away a fierce effort that required the United goalkeeper's intervention.

The Argentina international stopped captain Noboa's drilled strike moments later, giving the 350-odd visiting fans cause for encouragement and United another warning shot.

Ibrahimovic glanced a header over but groggy-looking Blind's exit seemed to rattle United's defence, with Eric Bailly throwing himself in front of a Dmitri Poloz shot.

There was a palpable release of tension in the 70th minute as United broke clinically.

Mata intercepted the ball just inside his own half and made a beeline for the box. Mkhitaryan swung in the cross for Ibrahimovic to flick into the Spaniard's path and he made no mistake from a matter of yards.

Rostov were not going to kowtow to United, though.

Bukharov, one of only three outfield players named on Rostov's bench, beat Bailly to send a header goalwards, forcing Romero into a fine 79th-minute stop.

The United goalkeeper again had to be at his best to stop Noboa scoring a stunning late free-kick - the last moment of a night when Mourinho's men underwhelmed.