Larkin secured victory with his second and Mansfield's third goal seven minutes into the second half, racing clear on to Lee Howells' misplaced pass and finishing confidently.
Lee Williamson and Wayne Corden then struck the woodwork from distance and young keeper Shane Higgs denied Larkin a hat-trick with a breathtaking save as the Robins faded badly.
Five minutes from time, Mansfield completed the rout, Darren Jones fouling Liam Lawrence and the wing man getting up to score from the spot, his ninth goal of the season.
Ironically, the goal was a carbon-copy of a dream start for the home side when Jones again fouled Lawrence.
Despite the setback of conceding the early goal, Cheltenham looked far more dangerous with the pace of Paul Brayson causing panic in the home defence. From one breakaway his shot fizzed narrowly wide and then his half volley was well held by the diving keeper.
Kevin Pilkington then clung on to a fierce John Finnigan 25-yard snapshot as Mansfield struggled to get out of their own half.
The best save of the game came at the other end though. Junior Mendes and Larking linked superbly in a flowing cross-field move and Corden's close range blockbuster was acrobatically punched over by Higgs.
The keeper repeated his heroics to deny Neil MacKenzie, but he had no chance in first half injury time when Larkin headed in Corden's deep cross.
At the other end, Grant McCann's low drive was tipped around the woodwork by another fine Pilkington save and with the last kick of the first half veteran Bob Taylor somehow scooped over the bar from six yards.