Although Rashford did not add to his scoring tally for the season, which stands at five goals in nine games overall, Mourinho was particularly pleased with the 19-year-old's defensive work on the flank.
"Marcus was phenomenal, he was phenomenal. Cedric [Soares] is a very good offensive full back, and [James] Ward-Prowse is a good crosser of the ball, so it was a good side," he told Sky Sports News. "Marcus felt what everybody else felt in the team - if we don't concede we win three points, so let's fight hard not to concede."
Lukaku proved the difference at St Mary's Stadium thanks to his sixth Premier League goal in the same number of games since joining from Everton.