Jimmy Floyd Hasselbaink enjoyed a dream start as Northampton manager after a goal inside the first 30 seconds of his reign was enough to see the Cobblers beat Doncaster 1-0.The former Chelsea striker was taking charge of his first game after replacing Justin Edinburgh this week, and saw his new side post their first points of the League One campaign.It took just 21 seconds for the Dutchman to celebrate the first goal of his Sixfields tenure, as George Smith raced down the left and set up Matt Crooks for a simple finish inside the area.Crooks spurned two further chances in a first half controlled by the Cobblers, but Rovers were much the better side in the second half, with Tommy Rowe and James Coppinger going close.Rovers laid siege to the Northampton goal in the last 10 minutes, and only an acrobatic save from Matt Ingram denied Ben Whiteman a late equaliser.But for all their aerial threat, Doncaster could not break down a Northampton side desperate to earn their new gaffer his first win.