That's the view of Sky Sports pundit Ray Houghton after the Blues - three points behind Premier League leaders Man City ahead of their clash on Monday evening - failed to score at home for the first time in 21 games.
Chelsea had 39 attempts on goal but could not break down a stubborn Hammers rearguard.
Jose Mourinho was scathing of the Irons' "19th century football" - but Houghton reckons the absence of Mata, who left West London for Manchester United in a £37million deal at the weekend, was one of the reasons the hosts toiled.
"Chelsea were lacking something despite having their big names out there - and perhaps they needed a Mata," the former Aston Villa and Republic of Ireland midfielder told Match Choice.
"Willian, Oscar and Hazard are very good at running at players and beating them with their ability and pace, but they didn't have someone who had that craft and creativity to pick out a pass.
"I didn't think there was an intensity about Chelsea, though, and I don't think they passed the ball with precision or quickly enough to unsettle West Ham defensively, but they should have put some of their attempts on goal away."
West Ham headed to Stamford Bridge having won just a solitary Premier League fixture - at fellow strugglers Cardiff - since the turn of the year, but were boosted by the return of Ivorian full-back Guy Demel and another start for fit-again striker Andy Carroll.
Houghton lauded the Londoners' defensive resolve but says they must show more attacking intent in upcoming games against relegation rivals Swansea and Norwich in order to propel themselves away from danger.
"Most neutrals would have expected Chelsea to have won as their form has been very good in comparison to the way West Ham have been playing, but I thought Sam Allardyce got his tactics spot on," added Houghton.
"West Ham didn't do much attacking - I think they had one shot - but they got numbers behind the ball, played narrow and frustrated Chelsea.
"They had more of a defensive shape, with Demel back and James Tomkins alongside James Collins at centre-half.
"There was a real unity about the side as well as players putting their bodies on the line time after time, while Adrian, in goal, was outstanding with his decision making.
"West Ham have got some confidence back but will need to show their offensive qualities in games coming up so they will need Carroll back and scoring goals and the new players [Marco Borriello and Antonio Nocerino] to make an impact."