Going into the game on a three-match losing streak in the Sky Bet Championship, the visitors dominated from the first whistle and fully deserved the success secured by two goals from Sam Saiz and one from Pierre-Michel Lasogga.
A delighted Christianson immediately dedicated the victory to midfielder Stuart Dallas, absent following the death of his mother.
He said: “Our thoughts are with Stewy and we wanted to put in a performance for him following the bad news that his mother had passed away.
“On behalf of myself, the players and staff, we send our condolences and assure him that this win was for him.
“I was very happy with the performance of the team. It is the same players who put us in the position we were in going into the match and today the difference was the intensity of our play.
“We knew we were up against a good side and that probably helped. We needed to be brave and believe in ourselves. The early goals were important and today we took our chances, whereas in other games we should have been ahead, but failed to score when we might have.”
Leeds took a fourth minute lead when Lasogga slid the ball into the path of Saiz, whose right-footed shot from inside the box appeared to take a deflection to beat Frank Fielding.
Ten minutes later the Bristol goalkeeper chose to make a challenge with his feet only for the ball to run into the path of Saiz, who fired home from 12 yards.
Lasogga capitalised on poor marking to head home a Kalvin Phillips corner to complete the scoring after 67 minutes.
Both sides were reduced to 10 men near the end when Leeds full-back Gaetano Berardi was sent off along with City substitute Matt Taylor for an angry confrontation following a foul by the visiting defender.
Christiansen added: “I didn’t see what happened for the sending-off, but the referee told me afterwards that he had no choice. He said my player was provoked, but that is not an excuse because you need to control yourself on the pitch.”