Louis van Gaal has experimented often during his tenure as Manchester United manager so far, and he continued to do so during his team's FA Cup win over Cambridge United at Old Trafford on Tuesday night.The formations doing the rounds once the starting XIs had been announced showed Marouane Fellaini in midfield and Wayne Rooney up front with Robin van Persie. When the teams lined up, though, United were playing a 4-4-2 diamond with Rooney in midfield and Fellaini lurking around the box.The formation was extremely flexible. Ostensibly, it looked as if Daley Blind was playing at the base of the diamond with Juan Mata at the tip, Angel Di Maria on left and Rooney on the right. Continuing the "square pegs in round holes" motif, Patrick McNair played at right-back instead of his usual centre-back.It was not just the roles on the pitch that struck an odd note as the game began. Intuitively, it seemed that United's best approach would be to lean heavily on their superior technique, using fast interplay and one-touch passing. Instead, with Fellaini up front, United looked to play a direct brand of football.Perhaps Van Gaal and his staff had identified a specific weakness in Cambridge's side, because the counter-intuitive approach soon paid dividends. Juan Mata opened the scoring in the 25th minute after a move that combined the best of both worlds in terms of United's style.McNair, impressive all game, fed Mata, who in turn slipped the ball wide to Di Maria. The Argentinian found Fellaini at the back post to nod the ball down to Mata, who had found his way into the box and tapped in the goal from close range.United's second also came via a cross to Fellaini, who was given far too much room in the box from a corner. The rebound from his shot was neatly crossed in from Van Persie to Marcos Rojo, and the Argentina international guided his header past Cambridge's 'keeper and a defender on the line.Van Gaal's unorthodox approach to dealing with League Two opposition at home had proved its worth. From that point forward, it was easy sailing for United. The home side dictated the game, finishing the 90 minutes with a 66.2 possession percentage.That dominance was reflected in the number of shots as well, as United out-shot their opponents 24-9. Di Maria and Mata were instrumental in creating chances, as they finished with four and three key passes, respectively. Fellaini contributed his share too, with three key passes.Mata was exceptionally tidy in his use of the ball, managing 96.8 percent pass completion from his 63 passes, according to WhoScored.com. That compared favourably with an out-of-sorts Rooney, who gave the ball away 17.7 percent of the time he attempted a pass.Rooney's midfield performance was underwhelming again, just as it was for most of January. If he and Fellaini looked to be playing in each other's positions, it was the Belgian who made a better fist of the role reversal. This makes sense given Fellaini has spent a good deal more of his career playing up front than Rooney has playing in midfield.Van Gaal chose a formation that allowed him to play Mata, Rooney, Di Maria and Van Persie in the same side, but there is no doubt he sacrificed balance in midfield to do so. The limitations of the opposition meant this was not exposed, but United still do not look like the finished product.However, in the FA Cup, victory is all that matters. As Van Gaalsaid so himself."In the Netherlands we have a saying: Death or the Gladioli which means all or nothing," the Dutchmansaid, via James Nursey of the Daily Mirror. "Its a Gladioli game [aay to the League One side]. You are dead or you receive the gladiolus flower and in cup matches its always like that."And on this occasion, the Iron Tulip's unusual approach ensured United were on the flowery end of that proposition.All statistics per WhoScored.com.Read more World Football news on BleacherReport.com Click here to read full news..