Following a difficult start to their PL return, Leicester appointed the relatively inexperienced Van Nistelrooy, and while the Dutchman may only have one English top-flight victory under his belt as a coach - ironically, a recent 3-0 victory over the Foxes as Manchester United interim boss - he has plenty of PL pedigree as a player.
Similarly experienced, Jamie Vardy gave his new boss the perfect start when played in by Bilal El Khannous, keeping his cool to slot past Lukasz Fabianski.
The strike was historic on two counts – firstly, Van Nistelrooy becomes the third manager in PL history to see his new side score within two minutes of his first match in the division, while Vardy has now scored the first goal under a record six PL managers.
Vardy then almost added another when Fabianski denied him from close range, but there was otherwise little threat from an albeit resolute Leicester side before the break. Instead, the Hammers threatened, with Danny Ings’ header deflected onto the post by Kasey McAteer and Mads Hermansen twice denying Jarrod Bowen.
West Ham remained positive after the interval, as Tomas Soucek fired over before Hermansen tipped over Mohamed Kudus’ deflected attempt.
The Leicester goalkeeper was almost the villain when the ball landed in the back of the net after his fluffed punch, but it was fortuitously ruled out for a Souček foul on the shot-stopper.
That decision ultimately proved pivotal, as within seconds, Leicester doubled their advantage. McAteer was released down the wing before playing in El Khannous, whose first-time finish for his maiden PL goal left Fabiański with no chance between the sticks.
The under-fire Julen Lopetegui’s situation was almost made worse when only a point-blank Fabiański save stopped Wilfried Ndidi from extending the hosts’ advantage further.
Eventually, Patson Daka struck the final blow, hammering into the roof of the net in the final minute of normal time.
Although Lopetegui can take positives from the chances created, including a late consolation from Niclas Fullkrug, a managerial change may well be on the cards at West Ham, with the Irons winning just one of their last five and ending the match only six points above the drop.
Leicester, meanwhile, will be delighted to end a run of seven competitive matches without a win, and are now just two points behind West Ham in the table.