The intense rivalry between supporters of the two London clubs has been turbocharged this season by their keen competition for the Premier League title. With six games to play, the Blues lead Spurs by four points. They will still lead Spurs by four points regardless of what happens at Wembley but psychologically speaking, victory for Chelsea could have a knock-on effect that might ease fan nerves at Stamford Bridge at a time when they have become frayed.

Antonio Conte's side go into the match on the back of a poor showing at Old Trafford where they slumped to a 2-0 defeat. They were also beaten 2-1 at home at the start of the month by Crystal Palace, a shock result that brought with it the first flurry of suggestions that their position as champions elect was fallible. Sandwiched between these games were two welcome victories over Manchester City and Bournemouth but despite this, the nagging doubts created by the wobble in form means that Conte will have had to spend time this week preparing his squad mentally as well as tactically.

Tottenham manager Mauricio Pochettino has no such problems. Spurs arrive at Wembley on an eight-game winning streak in all competitions in which they have scored 28 goals scored and conceded four. To say Pochettino's side have momentum would be an understatement. The Argentine also masterminded a 2-0 league victory over Chelsea in January, a result that abruptly ended the Blues 13-match unbeaten run in the top-flight. If the Blues are to stop Spurs in their tracks, Conte needs to refocus his players and reinstall the belief that propelled them to the summit of the Premier League.

Of course, Conte is well-versed in the art of manipulating footballers' mindsets. He did it on his arrival at the Bridge when he transformed last season's de-motivated losers into determined winners.

Two players who appeared to benefit the most from Conte's passionate management style were Eden Hazard and Diego Costa. Both players were out of sorts during the turbulent 2015-16 campaign, but they were reinvigorated over the summer and made telling contributions as Chelsea surged to the top of the league. Unfortunately though, while Hazard's star has continued to shine brightly enough for him to be nominated once more for the PFA Player of the Year award, Costa's season appeared to fizzle out in January in the wake of a row with a fitness coach and a big money offer to play in China.

At that time, Conte took decisive action and dropped the 28-year old striker for one game, a league match with Leicester City at the King Power Stadium which Chelsea won 3-0. The Blues boss deployed Hazard as a false 9 and flanked the Belgium international with Willian and Pedro. The result spoke for itself. Nevertheless, Costa was soon back in the side but he has flattered to deceive ever since.

Having failed to score in his past five games, Costa now has the look of a player whose career with a club has run its course. Despite non-stop stories linking him with a move away from the Bridge and his poor form, Conte has surprisingly persisted with selecting the forward and defended his performances to the hilt, giving no hint whatsoever that his place in the starting XI is under threat.

If Chelsea are to beat Tottenham, Conte cannot afford to gamble. The question is: what is in his mind right now? What does he consider to be a gamble? Playing Costa, or dropping him and going with Hazard as a false 9?

There will be no hiding place for Costa at Wembley should he fail to raise his game to the standard of which he is capable. Three years ago, in his first season with the Blues, Costa scored in a 2-0 League Cup final win over Spurs there. Against the same opposition in the same stadium, he has a gilt-edged opportunity to rise above the storm of recent weeks and attain hero status once more with Chelsea supporters.

Whatever Conte decides to do regarding Costa, he will keep his own counsel to avoid giving Pochettino the chance to adjust his game plan until as late as possible. It may well be one hour before kick-off when the team sheets are revealed before there is clarity on the situation.

In a team game that features 11 players on two sides, it seems crazy to think that just one of them might hold the key to the outcome. Right now though, in respect of the game between Chelsea and Tottenham it seems that Diego Costa is that man, and the pressure is on Antonio Conte to make the right call.