Carlo Ancelotti's Blues will lift the Premier League title if they pick up three points at Stamford Bridge, with anything less opening the door for Manchester United to finish top.
Chelsea are firm favourites to earn the victory they require, especially as Latics have little left to play for after securing survival.
However, Wigan have already pulled off a number of shock results this season, including a win over Chelsea at the DW Stadium.
And Melchiot has warned his former club that the league has been so competitive this season that there are no easy matches.
"Last season, if the big boys like Chelsea, United and Arsenal were playing against teams below 10th spot in the league, they knew it wouldn't be difficult," said the Dutch defender.
"Now it's getting harder. They know now when they turn up and play against us that we can compete with them.
"That's one of the good things for us from the season - and one of the harder things for them to take.
"You look at the teams we've beaten like Chelsea, Arsenal and Liverpool, and take all the stuff we've done. I think it's looking really good for us.
"The Premier League has been very exciting this season. Everybody can beat each other and that's a situation that's developing all the time."
Melchiot is confident that Wigan will produce one of their better performances now they are definitely safe from the drop and not under pressure.
"It's a different feeling for us now," he explained. "Maybe over the last month or two people have been looking at the table and worrying a bit, but that feeling has gone now.
"We know now we're safe. We can go back to the feeling we had at the beginning of the season.
"That's a more enjoyable way to play and you can feel the anxiety of your fans when you are fighting for every point.
"The mood now is chilled. We've achieved our biggest target by staying in the Premier League.
"We also achieved it earlier than we expected and the worst thing would have been going into that game at Chelsea needing a win to be safe.
"It's been a tough season, but a very interesting one as well. I think we've learned a lot."
Melchiot's contract expires this summer and he has not yet given much thought to his future, although he believes he could offer Wigan at least one more season.
"I always make my decision at the end of the season and this year will be no different," he said.
"When the season is done - that is the time to deal with things like this.
"When you start thinking about things like this during the season, it can weigh on your mind and take the edge off your game. I have never done that in my career and I'm not about to start now.
"I'd like to think I have more than one more year in the old legs. I will know myself when the time is right, but I feel very strong.
"I still have the hunger, but it's not just about that. You have to be able to play the game that you want to play.
"If you're not as fit or as fast as you want to be, then the problems will start coming. But as long as you have your fitness and your pace, you are all right.
"I have played in all the big games this season, and the games against the teams around us in the league, so people can make their own judgements about me."