Finally, in Elie Baup's 500th match as Ligue 1 manager, someone succumbed to the temptation. The 58-year-old has become so closely associated with his favourite piece of apparel that it is a breach of French journalistic regulations to include him in an article without referring to him at least once as "l'homme à la casquette" (the man in the cap).

So when André-Pierre Gignac fired Marseille into a 2-1 lead at Ajaccio on Friday with an extraordinary volley from just outside the area, he knew that this was his chance: after scoring such a goal, he could get away with anything. So he charged across the pitch to the dug-out and clattered Baup across the head. "He nearly knocked my cap off!" Baup said.

Gignac did not decap his manager. Actually, he was not even trying to: what he was attempting to do was administer a fraternal pat but, like a barber who slits his customer's throat while intending to merely shave him, he miscalculatd the amount of force required and ended up looking like he was trying to remove Baup's hat, or even his head.

To some that was interpreted as an involuntary expression of the rage the striker had felt at being dropped for the previous four matches. More likely, it was just clumsiness: how apt for Gignac to follow up a superb feat of technical excellence – his best goal in three years at Marseille – with a basic lack of co-ordination. Besides, due to the cold in Corsica, Baup was wearing a beanie hat rather than his customary baseball cap so Gignac would not even have been hitting the right target. Again, not altogether untypical.

Still, chapeau to Gignac for a wonderful goal. A well-timed one, too, as Marseille badly needed to beat Ajaccio and Gignac's strike came just after the home side had hit a surprising equaliser to raise fears that Marseille were going to make things hard for themselves again.

Ajaccio have the worst home record in Ligue 1 and although they have enjoyed a slight upswing in performances since Fabrizio Ravanelli was ousted as manager and replaced by Christian Bracconi, their lack of firepower makes them beatable by just about everyone.

Marseille duly took an early lead through Dimitri Payet, who profited from fine work down the right by Florian Thauvin to shoot expertly into the bottom corner from the edge of the area. It was Payet's first goal since mid-August and signalled a welcome return to form for a persistently inconsistent player. But four minutes later Ajaccio drew level as Marseille's defenders gawked like dozy tourists as Grenddy Perozo headed Johan Cavalli's free-kick into the net.

It was the ninth match in a row in which Marseille had failed to keep a clean sheet and all the doubts that surfaced during their wretched October, when they went on an eight-match winless streak and tumbled out of the top three, came back to the fore. But so too did Gignac. He had already served notice that he was on song when, in the 21st minute, he curled a magnificent effort against the post from way out on the left wing. Then, in the 39th minute, after neat chest control and while seemingly heading away from goal, he pirouetted at the edge of the area and blasted a stupendous volley into the top corner. Marseille were back on Easy Street and Thauvin added a third to ensure they returned with three points that, with Paris Saint-Germain, Lille and Monaco winning, prevents them from losing further ground on the top three.

A top-three spot and Champions League qualification represents the minimum return for Marseille after a summer of investment in new players. Marseille's second-place finish in the league last season was hailed as Baup's greatest achievement since guiding Bordeaux to the title in 1999 (which, amusingly enough, was won at Marseille's expense in the final minute of the final day of the season when Pascal Feindouno scored a winner for Bordeaux at PSG who, as their left-back Francis Llacer later confessed, were quite pleased their defeat deprived OM of the title).

The manager has struggled with this term's assignment. His Bordeaux success aside, Baup has generally been regarded as a fine manager at making limited sides well-drilled and resilient, which is what Marseille were last season when their runners-up spot was attained despite them scoring fewer goals than relegated Troyes. The challenge this season has been different, to play with more of a flourish while integrating an array of exciting young recruits. They have struggled.

At least in the Champions League they have a good excuse: they were never likely to advance from a group featuring Arsenal, Borussia Dortmund and Napoli and, sure enough, their chances of even reaching the Europa League are all but gone with two games still to come. So while Tuesday night's game at the Emirates is vital for Arsenal it is pretty much a dead rubber for Marseille; but that does mean it is entirely without significance for Baup. The manager will likely use it to give further experience to the gifted youngsters who have not quite shown enough to convince Baup he can definitely do without older campaigners such as Gignac, Benoît Cheyrou and Souleymane Diawara.

Some of the changes he makes for Arsenal have been enforced – Payet and André Ayew are injured, and Gignac and Mathieu Valbuena have niggles that may keep them out even though they have travelled with the squad. But others will be born of the manager's desire to see players emulate Thauvin, the 20-year-old who started the season sluggishly but, over the last month, has begun to justify all the hope and money invested in him when he was prised from Lille in the summer.

Like Thauvin, Mario Lemina was bought by Marseille last summer after helping France to victory in the Under-20 World Cup but the midfielder has yet to start a match this season. That will probably change at Arsenal. And then there is the curious case of Gianelli Imbula, the 21-year-old who was bought from Guingamp in the summer and is so highly rated that local media continually claim that Chelsea are preparing an enormous bid to take him away already. Yet he has hardly played over the last six weeks, being among the first players to be discarded by Baup when performances dipped in October.

Imbula played well against Arsenal in the opening Champions League group game and scored the decisive goal in a 2-1 win against Saint-Etienne. But Baup appears to believe he is not ready to be trusted regularly, an opinion seemingly shared by France's Under-21 manager, Willy Sagnol, who recently dropped him for unspecified disciplinary reasons. Imbula is likely to start at Arsenal, too. Impress there and he may just re-establish himself in the league, which is now Marseille's priority.

Jordan Ayew could start up front instead of Gignac, not so much to preserve the older player for the league but because the manager, you suspect, really wants one of his young forwards to start producing performances that make it possible to leave Gignac out for good. If his goal at Ajaccio is the most recent memory that clubs have of him, then that might help Marseille sell Gignac in January.