The victory puts United on course for this month's final with Ajax Amsterdam.
He has scored 11 goals in all competitions this season, including the extra-time victor to get his side past Anderlecht and into the semis.
Manchester United beat Celta Vigo in the first leg of their Europa League semi-final thanks to a Marcus Rashford free-kick.
The away goal could prove crucial but the narrow winning margin means Mourinho will, as suggested on the eve of the first leg, rest several players when United return to Premier League action on Sunday.
"I'm very pleased with the performance, not so pleased with the result", declared Mourinho. "At half-time [it] should have been three or at least two, but the result is open", goal.com quoted Mourinho as saying. Also, we play at Old Trafford, in front of 75,000 people, so we have to give everything on Thursday. "We tried until the end to win the match and score goals but we missed chances".
'The players that are in accumulation, they are not going to play next weekend'.
The first major European semi-final in the Spanish club's history began with a 1-0 first-leg defeat thanks to Marcus Rashford's splendid free-kick.
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Injury-hit United had also only won twice in 22 visits to Spain and knew they were in for a tough battle in Galicia.
Alvarez came to Celta's rescue once again in the 35th minute as he produced a good save to deny Henrikh Mkhitaryan in a one-on-one situation.
Celta's talisman and former Liverpool star Iago Aspas flicked a header just wide after the break, before Sisto saw his deflected shot tipped over the bar by United goalie for the night Sergio Romero.
And Owen believes United are better with the teenager than with Ibrahimovic. Rashford strode away and drew a foul from Hugo Mallo 25 metres out.
"He worked really hard and caused them problems. he had a fantastic shot in the first half, and then that attractive save".
By that time, the 19-year-old had made the telling contribution, curling a free-kick inside the far post from the right of the Celta penalty area.