If West Ham had to pinpoint a moment their season turned from being absolutely wretched to merely mediocre, then a 1-0 win over Chelsea in December, thanks to Marko Arnautovics first goal for the club, would probably be it.
Back then, the Hammers were one point from the Premier Leagues basement and without a win in more than two months. But ahead of Mondays clash at the London Stadium with Arnautovics previous employers, Stoke, West Ham find themselves with a six-point cushion over the relegation zone while the visitors — 13th at the time of West Hams season-shifting win over Chelsea — find themselves second from bottom.
Making these last few months doubly painful for Stoke fans has been the fact that it is their former hero Arnautovic, more than any other player, who has spearheaded the East Londoners recovery.
The crucial decision made by manager David Moyes ahead of the Blues visit last December was to move the moody Austrian off the wing and into a centre-forward position.
Until that point, the clubs record £24m summer signing had been deployed on either flank in 11 appearances. He had neither scored nor assisted, while West Ham had mustered just 10 goals and accrued three points from a possible 33.
Pushed up into a central position, however, Arnautovic has been a different player. Within nine minutes of the switch he was off the mark and since then he has amassed a further eight goals and four assists, while West Ham have secured 29 points from a possible 39 and have scored 22 goals. Only one of those goals — against Watford at home — came in a game when he started on the wing.
Following the positional switch Arnautovic has enjoyed the best goalscoring form of his five seasons in England, with nine goals in 25 appearances at an average rate of 0.5 goals per 90 minutes.
In total output, his best season came two years ago at Stoke when he scored 11 goals. Yet those came from 2,819 minutes on the pitch — at a rate of 0.39 goals per game — whereas this season he has so far featured in just 1,793 minutes.
Where his 2015-16 season does outshine his current campaign, however, is in the amount of goals scored against top clubs and the number of points his strikes won for his team.
Arnautovics goals have been directly responsible for four points this season, whereas in his best Stoke season he single-handedly won 15 points. His opener against Chelsea is his only goal against a current top-seven side this season; two years ago, five of his 11 goals came against sides who occupied those positions at the end of the season.
At Stoke, Arnautovic was occasionally played centrally but was overwhelmingly preferred as a left winger, from where he scored 19 of his 26 goals for the club. Prone to cutting inside, just three of those goals came from his left boot.
Approaching the target from a different angle at West Ham means he has already scored four left-footed strikes. Despite a sizeable 6ft 3ins frame, the 28-year-old is yet to score a headed goal in the Premier League.
Yet where Arnautovic may be slowing down at West Ham is in providing chances for his team-mates.
He currently averages 0.22 assists per 90 minutes — marginally better than his last two seasons at Stoke — yet his number of chances created has more than halved from 50 to 23. Last season he averaged 1.65 chances created per game and in previous seasons reached as high as 1.97, but this season that rate has dropped to 1.15 per game.
If it did not already look like good business, another goal or assist on Monday night will make £24m seem even more of snip if it puts Arnautovics new club on the brink of securing survival – and his old team on the cusp of relegation.