United were awarded a spot-kick in added time at the end of the first half of Sunday’s game at Old Trafford after Rashford went to ground following a challenge from Swansea goalkeeper Lukasz Fabianski.
However, television replays suggested that the England international was already on his way down before Fabianski made contact and the incident drew fierce criticism from Swansea head coach Paul Clement.
Red Devils manager Mourinho, though, offered his backing to Rashford after the incident which enabled Wayne Rooney to open the scoring.
“I don’t have a view because I didn’t watch,” said Mourinho. “And I have Marcus’ opinion and he said that the goalkeeper touched him.”
Clement was adamant that Rashford had "deceived" referee Neil Swarbrick, telling BT Sport : "My players clearly thought it wasn't a penalty and, seeing the replay, the player has deceived the referee. It's clear. There's no other way to look at it.
"The ref seemed to have some doubts because there was a big delay and I spoke to him afterwards and he said he was only receiving confirmation from his assistants. It was a mistake. He went down way before there was contact."
Relegation candidates Swansea salvaged a point thanks to Gylfi Sigurdsson’s superb second-half free-kick, but the Rashford incident was the game’s biggest talking point.
The 19-year-old is currently leading the United line in the absence of the injured Zlatan Ibrahimovic and he received the support of both Gary Neville and Michael Owen.
In response to Mourinho’s comments, former United captain Gary Neville tweeted: “He doesn’t need to justify himself for winning his team a penalty!”
He Doesn't need to justify himself for winning his team a penalty ! https://t.co/x5b6AXbBLe— Gary Neville (@GNev2) May 1, 2017
Ex-United striker Owen, meanwhile, accepted that it was not a penalty, but drew on his own playing experience to explain why Rashford would have gone to ground.
Owen told BT Sport : “Unless you’ve been in the same position, it’s very hard to explain.
“I was at White Hart Lane and I never did that, and I ended up breaking my foot. Paul Robinson, the goalkeeper, broke my foot and that turned into a knee ligament injury and I was out for a year-and-a-half because I didn’t protect myself.
“I planted my foot and then, once you’ve planted your foot, you’re not in control.
“It’s not a penalty, but I’m hesitant to say it’s a dive as well. It’s turned into one and it looks like one but, having been in that situation, you’re more protecting yourself than trying to cheat everybody.”