Former Arsenal, Chelsea and France striker Olivier Giroud had given the French club an interval lead with a stunningly-crafted volley on the stroke of half-time.
But after spurning several second-half chances, the Hammers – with skipper Jarrod Bowen looking especially lively – finally levelled when Niclas Füllkrug sidefooted home a richly-deserved equaliser with just three minutes left.
“It was a good work-out and it’s been nice to finish on a good note following a positive few weeks for us,” said Hammers boss Graham Potter after seeing his side draw 1-1 before prevailing 5-4 on penalties against the club that finished fifth in France’s Ligue 1 last season.
“I was pleased with the spirit of my team who were up against a good side that played UEFA Champions League football last year.
“We’d opportunities to score in the first half and it was pleasing we kept going to create some good chances after the break, too.
“Our attacking play was a big positive and we responded well in the second half against a talented team.
“Niclas would be the first to say he could’ve done more early on but he kept going, created opportunities and eventually got his goal. He brings a focal point to the team and is a goal threat, too.
"If Niclas can sustain a level of intensity then his quality will be a real asset for us this season.”
Having just forced the shoot-out, Füllkrug saw his opening penalty saved by Arnaud Bodart but after the next eight spot-kicks were all converted, Alphonse Areola spared the German’s blushes when he denied Nathan Ngoy.
Maximilian Kilman then expertly converted the first of the sudden-death kicks before Areola thwarted compatriot Lilian Baret to give West Ham a 5-4 victory.
Certainly, those two match-winning penalty saves proved timely for the French stopper, who had earlier seen Mads Hermansen introduced to the fans - packed into the sold-our lower tiers - after becoming West Ham’s fifth permanent signing of the summer following a reported £18 million move from recently-relegated Leicester City.
“We’ve done our research and got a young goalkeeper who has already got some experience of the Premier League,” added Potter after handing the 25-year-old Dane the number one shirt upon his arrival at London Stadium.
“Mads has got his best years ahead of him and he’ll add real competition, which is just what we need. He’s a good signing for us.”
Pre-season done and dusted, Potter now turns his attention towards the big kick-off against newly-promoted Sunderland at the Stadium of Light on Saturday (3pm).
“All credit to the lads for the way they’ve approached everything in pre-season – they’ve been open and responsive to what we’re trying to achieve and we’ve all had chance to connect. There’s a good, positive feeling around the place,” he said ahead of his first full campaign at the Hammers helm.
“There’s always room to improve, though, and we mustn’t get carried away. We’ve now got to regroup and focus on the Premier League. Sunderland represents a big challenge and we need to be ready for it.”