There’s little doubt who the star of Chelsea’s superb start to the season is. Diego Costa’s seven goals in his first ever four games for the Blues helped Mourinho’s side to maximum points from their opening four fixtures in the Premier League. A ruthless striker was the missing ingredient from Chelsea’s push towards the title last season with Fernando Torres, Demba Ba and Samuel Eto’o all failing to consistently find the back of he net.

Jose Mourinho’s solution this summer has certainly been ruthless as he offloaded all the three misfiring forwards and replaced them with Costa, Loic Remy and Chelsea legend Didier Drogba. It’s the Brazilian-turned-Spaniard that has caught the eye the most, but for how long will his rich vein of form last?

In the past few months, Costa’s hamstrings have been causing a bit of a bother resulting in a below par World Cup campaign. This week, the striker himself said, “There will be a moment when I cannot score – that is football.’’

Is this patch of form a sign of things to come or is it just a purple patch that will fail to last the season?

Here are five players from recent years who started their career with their Premier League clubs at a canter only for their performances to fizzle out into mediocrity.

Elano Blumer 

Manchester City paid £8 million to get the Brazilian from Ukrainian side Shaktar Donetsk and his initial performances under Sven-Goran Eriksson were hugely encouraging. His versatility meant that he was utilised in a number of positions be it playing on wing, in the number ten role, in central midfield or even at times at full-back.

Throughout his two seasons in Manchester, Elano always started the first few matches on a great note but his form eventually tapered off. During his first season he had already found the net four times by mid-October and in the first two games of the following season he registered three goals.

The winter weather in England seemed to affect his game badly as Elano actually rediscovered some form in March during his first season. In total, he scored six Premier League goals from March onwards in both seasons. Interestingly, from the month of November till the end of February, he only found the net once whilst in England.

One must not forget that he previously played in much colder Ukraine so his sudden loss of form can’t really be attributed to climate.

A player that was regularly praised by his Swedish manager, Elano ended up being shipped out to Galatasary after 24 months in the sky blue shirt.

Deco

Considered one of the best midfielders in the world when joining Chelsea in 2008, the Brazil-born midfielder had already won all that there’s to be won in club football when he arrived on the British shores.

Two stunning goals in his first two games earned Deco the Player of the Month award for August 2008 as Chelsea scored five goals without reply. Unfortunately for the Blues, their season quickly took a slump mirroring the Portugese midfielder’s form. New coach Luiz Felipe Scolari got the sack in February and Deco only scored once more till the end of the season.

Deco looked worryingly off the pace in the Premier League and it’s a shame that one of the best passers of the game couldn’t reproduce his excellent early form.

Robinho

The Brazilian forward was to be the first of a long line of established world-class stars to grace the grass of the City of Manchester Stadium (later renamed Etihad Stadium) after Sheikh Mansour’s the take-over. After all, £33 million is no small price to pay for any player.

Robinho’s start in the Premier League was truly exceptional as he scored for fun all kinds of goals – free-kicks, tap-ins and drives from distance. He seemed to have it all as he netted a hat-trick against Stoke City a few weeks after his debut. However, after finding the net 12 times in his opening 19 games his form took a steep decline with only three moe goals following until the end of his first season in England.

His second campaign took another turn for the worst as the Santos hero only managed one goal (against the mighty Scunthorpe in the FA Cup) before being shipped out back to Brazil on loan.

Amr Zaki

The Egyptian striker’s rise to goalscoring fame was just as abrupt as his decline. When the then 25-year-old arrived at Wigan Athletic in the summer of 2008 on loan from El Zamalek he already had 23 goals to his name with his national side. However, not many people outside of Egypt had heard of the powerful striker.

His start to life in England was explosive. By mid-October he had scored eigh goals in just 10 games whilst playing in a very limited Wigan side under the guidance of Steve Bruce. Another three goals by the end of the 2008 calendar year followed adding fuel to transfer rumours linking Zaki to some of the top clubs in Europe.

Unfortunately, at the turn of the year things changed dramatically. 13 games in 2009 for Wigan produced zero goals. Furthermore, discipline problems also came into play as Bruce heavily criticized Zaki for returning late from international duty.

Wigan didn’t pursue their interest in Zaki after his one-year loan deal expired and a six-month loan with Hull City in 2010 also ended goalless.

Harry Kewell 

The Australian winger had made a name for himself at Leeds for his technique and a wand of a left foot that more often than not produced the right pass in the final third. His controversial move to Liverpool started off at a canter as the Australian quickly bought in to Gerard Houllier’s playing style.

His first goal in a Reds shirt couldn’t have arrived in a better game as it came in the Merseyside derby against Everton in a 3-0 victory at Goodison Park. 11 goals in all competitions was a decent return for the winger with most Premier League strikes coming early in the season.

Unfortunately, Kewell would never reach similar heights with only five other goals being scored in the following three seasons. Admittedly, injuries hampered his progress but it’s hard to believe that the Anfield side had to fend off interest from European giants Barcelona and AC Milan to get their man.

At the end, Kewell’s expensive wages only brought eight Premier League assists in four years. His Leeds career and the first few games at Anfield had promised so much more!