Diego Costa Dimension Poses Different, Menacing Problems for Chelsea Rivals

STAMFORD BRIDGE, LONDON — "Welcome to the top of the league," the Chelsea pitch announcer has declared with gusto ahead of every home game this season.

By virtue of their lofty league position this Christmas, West Ham United needed no such introduction to the Premier League's summit.

Remaining in the top four heading into the festive period, Sam Allardyce's side have had more than a taste of life in the top-flight's leading pack.

What they hadn't experienced until their trip across London was what it takes to remain there.

Now they know.

Matt Dunham/Associated Press

Chelsea were mesmerizing at times here, putting in a performance that was in stark contrast to that of last season, when the Hammers frustrated them.

That game in late January finished 0-0—it's remembered more for Chelsea boss Jose Mourinho's views on West Ham's "19th-century football"—but with Diego Costa now leading the line, Chelsea are a different beast altogether these days.

"There is no perfection, but we played very well against a difficult team, which is more difficult," Mourinho said at the final whistle.

"We played very well against two different versions," Mourinho continued. "The first one against a defensive side and we were very good—we moved the ball, we moved the players. ... In the second half, against another version, against an attacking team, a team that tried to put pressure on us."

It was the case last term, too—a fact outlined by Chelsea finishing with 39 shots on goal. They couldn't find a breakthrough, though, lacking presence and guile with their front men.

Diego Costa's addition has changed all that, and Chelsea now have an end product for all their dominant play in the opposition half.

The Spain international not only scored against the Hammers, but he also earned himself an assist for John Terry's opener by heading the ball into the captain's path for a simple tap in.

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Sam Allardyce's side frustrated Chelsea up to that point, and the Blues needed some inspiration. That is exactly what Costa gave them with his quick movement to react quickest to Cesc Fabregas' corner.

We've seen Costa's wonderful forward play already season, yet given the struggles Chelsea faced against the same opponents almost 12 months ago, this win was the final declaration we've needed of his prowess.

Given how that draw last term defined Chelsea's failure in the title race, facing West Ham was almost a barometer for how this new-look side has developed since.

Now the signs are good.

Matt Dunham/Associated Press

Costa's desire to chase every ball, to make those darting runs into space and bully centre-backs is reminiscent of Didier Drogba in his prime.

He's what Chelsea needed more than anything else after blowing the title last season, and here he is now, helping to all but deliver it.

"I think we are a much better team when we have the ball," Mourinho said, outlining the difference between Chelsea circa 2013/14 and Chelsea today.

"Last year, we were very strong defensively, very organised," Mourinho said. "But there was a lack of creativity when we had the ball. The challenge this season was to bring that creativity and dynamic without losing the good defensive qualities of the team."

What the manager failed to mention is how Costa has been so influential in making that happen.

This is a Chelsea team with a different edge. There is a clinical look to Chelsea now—one that gives the impression they can score with every attacking move.

Clive Rose/Getty Images

If Costa isn't scoring, he's getting into positions that allow his teammates to benefit. He leads the line in the way a striker should.

In an age of false nines, it's fitting he is blowing the trumpet of out-and-out strikers in the Premier League—the very place they are supposed to flourish.

It's refreshing for neutrals as much as it is Chelsea fans. The agenda has been changed, with Costa's phenomenal ability right at the heart of it.

Mourinho's Chelsea are a menace once more.

Garry Hayes is Bleacher Report's lead Chelsea correspondent. All quotes were obtained firsthand unless otherwise noted. Follow him on Twitter @garryhayes