Celtic took control in the second half and goals from James Forrest and substitutes Odsonne Edouard and Ryan Christie took their Ladbrokes Premiership tally to 12 in two matches before Donnelly struck again in stoppage time.

The trip to Fir Park, where Motherwell had won nine of their previous 11 games, was an early test in Celtic's title defence given it came little over 48 hours after they returned from Romania.

Manager Neil Lennon made four changes following their 1-1 Champions League draw with Cluj. Nir Bitton and Christopher Jullien came into the back four for the suspended Jozo Simunovic and Hatem Abd Elhamed, who had a minor muscle problem, while Olivier Ntcham and Griffiths replaced Christie and Edouard.

Motherwell took the game to Celtic and Declan Gallagher headed wide from a corner before the hosts took a 12th-minute lead after another corner was cleared. Gallagher headed Liam Polworth's crossfield ball down to Donnelly and the midfielder volleyed inside Scott Bain's post from 20 yards.

Stephen Robinson's team did not have time to settle on their lead. Right-back Ajer drove forward from deep inside his own half and ran on to Forrest's return pass before beating the onrushing Mark Gillespie.

The hosts continued to make the running and had a penalty shout midway through the half when Ajer and Christopher Long went down in a tangle of legs. But the striker did not make much of the incident and referee Nick Walsh played on.

Celtic had a better spell and Boli Bolingoli volleyed just wide after Ntcham played the left-back in behind, although Motherwell were still using the ball well themselves.

Griffiths was handed the sort of opportunity he often laps up when Gallagher needlessly pulled him down as they competed for a long ball. Neither Motherwell's wall nor Gillespie protected the far corner and Griffiths drove the ball low into the net.

The hosts attempted to reply immediately and Donnelly drove the ball across face of goal but Celtic had a greater control of proceedings as the second half started.

Lewis Morgan shot high over on the break before Celtic made their possession count in the 66th minute. Forrest collected Bolingoli's cutback and worked space to shoot in off the far post.

There was a touch of controversy about the fourth in the 76th minute as Motherwell appealed for handball against Bolingoli as the left-back controlled a pass before finding Ntcham, who squared for Edouard to slot home from 18 yards.

The hosts caused their own downfall for the fifth after losing possession following a goal kick. Donnelly brought down Edouard and Christie dispatched the 86th-minute penalty high into the net.

Donnelly grabbed his sixth goal of the season when he lashed the ball high into the net from close range following a corner.