Ibrahimovic had not scored in his last six Manchester United appearances heading into the clash in south Wales.
But he twice found the net before half time as United saw out the game with ease.
His first was also milestone in that it was the 25,000th goal scored in the Premier League.
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And Jose Mourinho, who kept faith in the Swede during his drought, said he always expected Ibrahimovic to score today.
"I knew that Zlatan Ibrahimovic would score,” Mourinho said.
“It was always a question of time.
“But one thing is a striker who does not score and does nothing for the team. He always does everything for the team.”
Ibrahimovic will miss United’s clash with Arsenal after the international break after picking up a yellow card.
Asked about the booking, Mourinho replied: “He will not play [in United’s next game] because of the yellow card but I did not see it, I don't comment on referees."