One of the crowning moments of Frank Lampard's career collided with bad blood from his formative years as his 200th Chelsea goal was met with a hail of missiles from West Ham fans at Stamford Bridge.
Substitute John Terry is understood to have been hit by a coin thrown from the section of the Shed End housing visiting supporters after former West Ham player Lampard scored the opening goal in an ultimately comfortable Chelsea win.
Missiles including drinks bottles, coins and other objects were hurled towards the Chelsea players as they celebrated, and the incident could yet lead to an FA charge if it is reported by referee Michael Oliver.
The Metropolitan Police confirmed they were investigating incidents of coin throwing, and officers were studying CCTV pictures to identify those responsible. No supporters were ejected or arrested but the investigation will continue.
Eden Hazard marked a superb performance with the second goal, and victory moves Rafael Benitez's side to third in the table, above a faltering Tottenham and within four points of Manchester City.
Domestic issues and local feuds dominated events at Stamford Bridge however, as West Ham fans reacted to the mildest of provocation from Terry and had their jeers rammed back at them by Lampard.
Even before the goal Terry, a substitute, had been targeted by coins and missiles from the visiting supporters as he chose to warm up in front of them.
Terry had again relegated to the bench by Benitez for a Premier League game but he still managed to find his way to the heart of the game's pivotal moment.
When Gary Cahill went down injured in the 17th minute Terry was off the bench to warm up with rare haste. With the assistant referee running the line at the Matthew Harding Stand end he headed in the direction of the away supporters.
Not one to shrink from a challenge he eyeballed the West Ham supporters abusing him and proceeded to perform a series of pointed exercises. He mimicked raising a trophy several times, and then turned to touch his toes leavings his backside pointing at the visitors.
While this pantomime was playing out Terry's teammates were concocting a far greater act of provocation. Hazard's shot was beaten out by Jussi Jaaskelainen as far as Victor Moses, who returned the ball to the Belgian to cross for Lampard, unmarked, to nod the ball home.
The former West Ham player was not about to let the moment of his 200th goal pass uncelebrated and as he ran towards the West Ham fans to celebrate he was met by Terry, galloping back down the touchline to join in.
"I wasn't hit by anything," Lampard said. "I went quite close to the West Ham fans but that was the natural curve of my run." As the game re-started Terry stopped to pick up several coins, and turned to display them to the travelling fans. Point made, though not to the satisfaction of fourth official Howard Webb, who instructed substitutes from both sides to warm up at the other end thereafter.
A West Ham spokesman said that anyone found to have thrown coins could be banned by the club.
"West Ham will be working with Chelsea to investigate the incidents of missiles throwing. Any individual found to have acted in an inappropriate way will have to face the consequences including the possibility of being banned from future matches."
As the home club responsible for controlling supporters Chelsea could also be charged. They were fined pounds 30,000 in 2005 after Matjai Kezman was struck by a coin thrown by a West Ham fan.
Benitez praised Lampard for his "fantastic achievement", but acknowledged that he could have celebrated in a safer corner of the ground.
"When you score 200 goals, you don't really think about where you go," Benitez said.
The antagonism was a distraction from a sumptuous performance from Chelsea. A fine Hazard pass created the first for Lampard, whose characteristic late run took bought him time and space to finish.
Hazard's goal was just as well-crafted. Starting on the right touchline he played a one-two with Juan Mata, brought down the return pass on his chest at pace and stepped inside two covering defenders before crashing his left-foot shot past Jussi Jaaskelaninen in the West Ham goal.
While Benitez goes into the international break hoping his players get some rest and return refreshed, Allardyce was left fretting with his side only six points clear of the relegation zone.
"I'm always worried until we're mathematically safe," he said. "My belief in our home record is that it'll be good enough for us to get safe."