Zemmama curled home a free-kick from a difficult angle to put the game beyond Jim Gannon's side 10 minutes into the second half.
Derek Riordan had put Hibs back in front moments earlier after Mark Reynolds cancelled out Colin Nish's early opener.
Zemmama was a constant menace as he started his first Hibs match since April 2008 after spending most of last season on loan with Al Sha'ab in the United Arab Emirates.
Goals were always on the cards as both managers set up with attacking formations. Nish's recall meant Riordan moved to the left side of a midfield four with Zemmama on the other flank.
Gannon had striker John Sutton back after injury and the Motherwell manager employed both his full-backs in advanced positions when Well had the ball.
The tactic backfired in the ninth minute as they were caught on the break after enjoying the bulk of the early possession.
Jim O'Brien lost the ball midway inside the Hibs half and the visitors broke down the right with Zemmama. Riordan volleyed the Moroccan's deep cross across the six-yard box and Nish cushioned the ball home despite John Ruddy's efforts to keep it out.
Steven Saunders forced a diving save from Graham Stack with a volley from Yassin Moutaouakil's free-kick but the Motherwell defender had a let-off in the 18th minute after misjudging a long ball.
Nish got in behind him and went down inside the box claiming Saunders had clipped his heel, but referee Steve Conroy waved play on.
Zemmama was twice off target from long range before his penetrating run was stopped inside the box by the backtracking Giles Coke.
Ross Forbes went close with a blistering 25-yard strike but Motherwell were slow to get the ball in the box.
Sutton looked capable of causing problems when they did and Well got a 35th-minute equaliser when Reynolds beat Stack to O'Brien's near-post corner to head home from close range.
Motherwell threatened from more set-pieces either side of the break but they paid the price for allowing Riordan space inside the box in the 51st minute.
Liam Miller dispossessed Coke and threaded the ball through for the unmarked Riordan, who slotted the ball into the far corner from 16 yards.
Conroy, criticised for handing out 11 yellow cards and two reds during last weekend's goalless clash between Kilmarnock and Rangers, issued his first booking in the 55th minute when O'Brien chopped down Ian Murray.
Zemmama further punished Well when he curled the free-kick inside Ruddy's near post as the goalkeeper anticipated a cross.
The Moroccan was fortunate to escape a booking after gesturing towards the home fans while being admonished by Conroy for celebrating in front of the East Stand.
Miller and David Wotherspoon were also booked but Hibernian's only real worry in the final quarter came when Miller cleared off the line from team-mate Sol Bamba following a corner.
Well were fortunate to escape conceding a penalty when Coke appeared to go through Miller with a sliding tackle as the former Celtic midfielder prepared to shoot.
And Zemmama almost set up another goal but Ruddy blocked from Danny Galbraith before fellow substitute John Rankin fired over from the rebound.