The Manchester United striker was keen to bounce back from his miss from the spot against Arsenal at the weekend, after being given the chance to give his side a 2-1 lead.
But the torrential rain caused his standing foot to give way at the crucial moment, a slip that could have sent the ball anywhere.
Fortunately for United and Rooney, the slip sent the ball in the opposite direction to Braga goalkeeper Beto, saving the striker's blushes of missing their fifth penalty of the season.
And Rooney admitted being relieved.
He said: "I was a bit fortunate; I slipped but thankfully it's gone in so I'm happy with that.
"At the time it happened so quick, but obviously I've seen it going towards the goal and the keeper going the other way.
"I was happy with it going in but obviously I've been quite lucky with that."
Rooney insisted he had no hesitation in taking responsibility for the kick, despite his miss at Old Trafford four days earlier.
"I had no doubts at all," he continued. "Obviously I was disappointed at the weekend, not only to miss but to miss the target.
"I said after the game it wasn't good enough."
But his success against Braga on Wednesday was good enough to secure United victory and top spot in group H with two games to spare.
It looked unlikely going into the final ten minutes with Braga leading 1-0 through a penalty given away by Jonny Evans.
But the introduction of Robin van Persie changed the game, the Dutchman equalising with a fantastic piece of improvisation to lift the ball over Beto as he inadvisably raced from his line.
And after Rooney's spot-kick, Javier Hernandez put the gloss on the result with a typical poachers goal in stoppage time.
Rooney continued: "I think we can play better football - at times it was too slow but the result is the most important thing.
"I think we had quite a bit of possession, we just needed a bit more movement and speed to our play, and thankfully in the last 10 or 15 minutes, when it mattered, we got them."
Ryan Giggs was in no doubt that the introduction of the £24million man changed the game.
He said : "It wasn't until Robin came on that we started to play a little bit better.
"His confidence is just sky high at the moment.
"I read last week that a lot of the players think he's similar to Ruud van Nistelrooy in the respect that Ruud used to get a chance and more often than not he'd put them away.
"That's the case with Robin at the minute; his confidence is high, we're creating chances for him and he's putting them away."