Man Utd head coach Ruben Amorim admitted "nobody expected" the magnitude of their 3-0 Europa League semi-final first leg win at Athletic Club but insisted the tie was still not over ahead of next week's return match.
His side became only the third to win at San Mames since August and inflicted the joint-biggest defeat on their hosts at the stadium in over a decade, putting one foot in the Europa League final at the same stadium later this month - where they look likely to meet Premier League rivals Tottenham.
United weathered an early storm from the hosts but took the lead through Casemiro's header, and then played much of the game with a man advantage after centre-back Dani Vivian conceded a penalty and was sent off for pulling back Rasmus Hojlund in his own box.
Despite scoring three goals in the final 15 minutes of the opening period, the one criticism of the visitors' performance was that they did not manage to add to their advantage and kill off the tie as a contest.
Man Utd are the only remaining team unbeaten in Europe this season, in stark contrast to their Premier League campaign where they have lost 15 of 34 league games - but even so, the head coach had not been expecting such an emphatic victory in the Basque country.
"It's the best result because nobody expected this result," he said. "But you saw two games today - the first 25 minutes and then, after the goal and the sending-off, the game changed.
"In the second half, we tried to be cautious and we created chances but the most important thing is the opponent didn't get many shots on our goal.
"We've improved in the last games. I don't look just at the results. We had some games that we won that we didn't play well and some games we lost but played well. Sometimes you need a little bit of luck.
"In the first 30 minutes, they had chances to score. If they score, it's a different game. When we scored, we felt more free to play.
"It's hard to understand but sometimes it's the context. We can win this competition. In the Premier League, we are suffering game after game. We try to manage both things with some injuries. Sometimes it's hard, even for the players."
Amorim sounded a note of caution despite the size of Man Utd's victory, and the meteoric collapse which would be required for them to be eliminated.
Of 133 previous first-leg away wins by three goals in European knock-out ties, all 133 teams have progressed to the next round.
But Amorim told TNT Sports: "We had the chances to score one more, but this is not done. The same result can happen at Old Trafford, and we need to be prepared."
Amorim: Hojlund's best game for me
Hojlund could not add to the last-gasp equaliser he netted at Bournemouth at the weekend but did put in a strong shift leading the line for United, proving an agile target man while also showing far better positional awareness than he has in recent games.
Amorim has kept faith with the beleaguered striker through his prolonged struggles this season, in part due to a lack of senior alternatives, and gave him a vote of confidence following his performance in Thursday's game.
"It was the best game he had with me as coach," he said. "He helped the team a lot. He secured the ball and made runs. It was a good moment for him but like Harry (Maguire) he needs to understand everything can change so let's focus on the next one. This one is in the past."
