On Wednesday evening, the two European juggernauts played out a thriller in Paris in a match that saw both teams come from behind to lead on different occasions.
The visitors initially took the lead through Raphinha, before former Barcelona man Ousmane Dembele and Vitinha turned things around at the beginning of the second half.
However, Raphinha's sublime second got Barcelona back on level terms before Christensen came off the substitutes' bench on his birthday to put the La Liga giants in front.
Xavi's side were able to come through the final 13 minutes plus added-on time without conceding a leveller, handing them the advantage when the teams reconvene at Estadi Olimpic Lluis Companys next week.
Barcelona dealt double blowNevertheless, that is not to say that Xavi and his Barcelona squad left Parc des Princes feeling totally satisfied with how things fare ahead of the return fixture.
At least one change will need to be made to the starting lineup courtesy of Sergi Roberto's yellow card in the 34th minute, taking him to three in this year's competition from just two starts and three substitute outings.
Christensen had only been introduced as a 76th-minute substitute, one minute prior to his goal, but the Dane would also collect his third yellow card of the tournament.
As a result, the pair will not be present in the squad for the home fixture, leaving Xavi with decisions to make regarding his selection.
Who could replace Sergi Roberto?Fortunately for Xavi, he has a number of options available to him, most notably Pedri who was making his first Barcelona appearance in
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