The Blues who visit third-placed Liverpool are six points behind leaders Manchester United who will visit Arsenal tomorrow.
Ballack told The Sun: “There are two big games with four big teams.
“We are six points behind and know if we lose any points it gets more difficult. We need the points to make the distance shorter.
“It’s a giant game for us and it could be the defining weekend of the season.
“I’ve been in this position before and there have been lots of moments in my career when things have changed quickly.
“But there are moments during a season that are crucial, that if you lose games it becomes difficult and if you win it’s easier. Maybe now is a big moment when the big decisions will be made.
“This is the time to push on. We have to come back and show Man United we’re back. It would be great for us to beat Liverpool.
“This weekend could be a big turning point. We could go to three points behind, stay at six points or go out to nine.
“We don’t want to lose points as the distance would be too big but it’s difficult for both us and Man United because we’re both away from home.
“If we can win, we will show we’re very strong and want to win the title. If we don’t win, what can I say?
“I remember when we won at Everton and United lost at West Ham on the same day. That made it a good weekend for us. We have to do the same again and put pressure on them.”