Luton earned their first Sky Bet League Two win of the season with a 3-1 victory at 10-man Cambridge.The first half an hour contained a succession of chances, with Luton the first to take one after 21 minutes. Against his former club Luke Guttridge ran on to a loose clearance and beat home goalkeeper Chris Dunn with a stunning lob from distance.The U's were level seven minutes later as defender Leon Legge powered a header past Mark Tyler from Mickey Demetriou's free-kick.The pivotal moment of the game came 20 minutes into the second half when Harrison Dunk handled a cross and received a second yellow card. From the resulting free-kick Luke Wilkinson met Danny Green's delivery with a downward header at the back post.Green then sealed the result with six minutes to go, calmly slotting beyond Dunn after good interchange between Guttridge and Craig Mackail-Smith.The result was Cambridge's third home defeat in a row in all competitions.