The Blues currently sit second in the table, four points behind league-leaders Arsenal, and travel to face struggling Sunderland on Wednesday night.
Manchester City and Liverpool are also in the mix and while both United and Spurs fell further behind the pacesetters after sharing the spoils in a 2-2 draw at White Hart Lane on Sunday, Mourinho feels they are both still protagonists in the Premier League title fight.
However, the former Real Madrid coach also believes eighth-placed United and Spurs in ninth will find it difficult to mount a challenge if they slip any further adrift of top spot.
"United are nine points behind Arsenal," he said.
"It is a gap. Tottenham are 10 behind. It is not a gap for us because we are speaking about five or six points, that is not a gap. It is something that in two matches can be over, but nine or 10 points is a gap.
"I keep saying that there is a lot of games to play in December and at the beginning of January we can have a look and see if all six are within shorter distances.
"Spurs and United know that if the next step is to reduce from 10 to seven or from nine to six it is to get them back in to the race, but they know that if the next move is from 10 to 13 it becomes hard.
"Arsenal are much more comfortable because they can slide in one match and nothing matters to them but some teams know the next slide could be crucial.
"The six teams are very equal in their potential. I see the six teams as very good teams and there are other teams doing very well. Everton and Newcastle are doing very well."
Mourinho refused to highlight a favourite from the six sides he believes are genuine title challengers but does think there is more pressure on City, given their abundance of talent.
"I don't think that we can talk about favourites but we can say that there is one team at the top of the league," he said. "All of the six teams are title contenders but I keep saying the club with the most pressure to win it, because their squad is quite unique, is Manchester City."
Chelsea face a trio of the Premier League's bottom five clubs in their next three games but Mourinho is not taking anything for granted, starting against Gus Poyet's Sunderland, who they also face in the Capital One Cup quarter-finals later this month.
"I was analysing their match against Newcastle at home and Man City at home, these were the matches I focused on," the Portuguese said.
"I think they are better than the points they have, the quality of their players is not comparable with some teams in that part of the table but I think they are in a moment where one point doesn't make a big difference.
"They need three points, they need two or three victories to get out of the dangerous area. I don't think they can play in a defensive way, that is why they have a positive approach because they need to win matches.
"I think Gustavo's style is to try and play good football, I think we have two very difficult matches."
Mourinho confirmed striker Samuel Eto'o could feature at Sunderland following a groin injury but the Blues will be without David Luiz and Oscar.
The Portuguese also expects Ashley Cole to start one of the next two games after the England international lost his left-back berth to Cesar Azpilicueta.