Sir Alex Ferguson believes Manchester United's showdown with Chelsea will 'go a long way' to establishing the Premier League pecking order.
United returned to the top of the table on Monday night after Park Ji-sung's first-half header secured a 1-0 win over previous leaders Arsenal.
The result ensured the Red Devils remain unbeaten in the league this season and they also have a game in hand on their title rivals.
Ferguson next takes his team to reigning champions Chelsea on Sunday and the United boss is aware of the importance of the Stamford Bridge clash.
"It's a massive game now," said Ferguson. "That will go a long way to establishing the top of the league.
"It's a big, big game for United."
The scoreline was the first time United had won 1-0 in the league this season and Ferguson believes such narrow victories will become key in the title race.
United won 10 games by that scoreline en route to winning the league in 2009 and Ferguson hailed the performance of Rio Ferdinand and Nemanja Vidic against Arsenal.
He added: "[Ferdinand and Vidic] were tremendous. That gives you a great foundation, and 1-0 victories can win you the league.
"If my back four keep that foundation of not conceding any goals it gives us a really good chance."