Remi Garde's men powered their way to the summit as they earned their first win at the Velodrome since 2009 thanks to the striker's magnificent treble
In what was initially touted as a battle of who could supersede Paris Saint-Germain at the top of the table, it was les Gones who raced into a commanding lead by the break courtesy of Bafetimbi Gomis' double, the first of which came from the spot.
Steed Malbranque's measured strike just after half-time put the visitors into a shock 3-0 lead and they put the result beyond all doubt when Gomis completed his brilliant hat-trick, notching his 80th Ligue 1 goal in the process.
Loic Remy netted late on for Marseille but Rod Fanni then saw a straight red for a late challenge as a night of misery was compounded for Elie Baup's side.
The fixture had been rearranged from October 28th on account of the the heavy winds which resulted in the original game postponed. It was almost called off for a second time earlier on Wednesday before a pre-match pitch inspection saw the match delegate give the game the green light. Nevertheless, an explosive and somewhat controversial start ensued as the match began in dramatic fashion.
A long pass into the path of Gomis led to Marseille goalkeeper Steve Mandanda pulling down the striker, giving referee Clement Turpin no option but to award a penalty after just three minutes. Gomis preceded to send Mandanda the wrong way and hand Remi Garde's side an early advantage.
On a slow and muddy pitch, neither side could control their passes accurately but Marseille almost posted an immediate response. Fanni's superb run on the wing found Jordan Ayew, whose fine header was somehow tipped over by Remy Vercoutre.
Baup's troops were noticeably better after going behind, but their lack of finishing remained evident as Jordan failed to capitalise on a shocking mishap between Anthony Reveillere and Vercoutre, with the young Ghana international unable to equalise.
Despite the home side's progress, it would be Lyon who would strike next, just after the half-hour mark. Mouhamadou Dabo's cross picked out Gomis, who shrugged off a diving Souleymane Diawara to expertly round Mandanda and fire powerfully into the net for 2-0.
Baup had decided to drop the sluggish Joey Barton at half-time, in favour of Loic Remy, but the change did not bring the comeback that Marseille had hoped for, as the visitors surprisingly raced into a 3-0 lead two minutes after the re-start.
A fine attacking move, started by Malbranque, saw the midfielder pick out Lacazette, who returned the favour with a fine cross before the former Sunderland and Tottenham man struck a superb volley to beat Mandanda and leave the Velodrome shell-shocked.
The visitors were utterly dominant - and even without the likes of Yoann Gourcuff, Lisandro Lopez, Jimmy Briand or Dejan Lovren - they almost drew further ahead. Once more, the hosts' defence was virtually non-existant as Lacazette raced into the box unopposed, before his low effort was parried away by Mandanda.
Garde's side continued to dominate and they surged further ahead when Reveillere latched onto Lacazette's pass on the over-lap and, despite a number of defenders, he still managed to pick out Gomis, who fired home with consumate ease to complete his hat-trick.
The hosts did get on the scoresheet, though, as Jordan Ayew's low cross was parried in the path of Remy, who fired in for his first Ligue 1 goal of the season. Nevertheless, Fanni only added to OM's problems when he was shown a straight red card for a late challenge on Dabo as Lyon won at the Velodrome for the first time since 2009.
The result sees Lyon go clear, two points ahead of PSG and Marseille, who remain third. The hosts, who suffered their heaviest home defeat for six years, now travel to Brest as Remi Garde's men welcome champions Montpellier at Stade Gerland on Saturday.