Ancelotti's side look to protect a 2-0 lead in the quarter-final second leg at Stamford Bridge against a Chelsea side reeling after three successive defeats.
Real are bidding to retain the Champions League crown, having knocked out then-holders Chelsea in the quarter-finals en route to lifting the trophy last season.
Chelsea's fortunes have changed dramatically in the 12 months since and they sit 11th in the Premier League, with their hopes of returning to the Champions League resting on winning the competition under interim boss Frank Lampard.
Lampard is Chelsea's third manager this season following the sackings of Thomas Tuchel and Graham Potter, while co-owner Todd Boehly reportedly told the players their season has been "embarrassing" following Saturday's loss to Brighton.
Despite their struggles, former Chelsea boss Ancelotti believes the Blues will still be determined to prove a point by stunning Real in the second leg.
"Chelsea has a difficult moment. I'm thinking the game tomorrow can be a great opportunity for them to move from this situation," Ancelotti told reporters on Monday.
"We're aware of this, we take it into consideration. We will try to play at our best.
"We're good. We're motivated as always. These are all important games. We have to have a very complete game.
"Ninety minutes remain and in this type of competition, anything can happen. We'll be ready to play at our best."
Real had to dig deep to survive against Chelsea in the quarter-final second leg in Madrid last season, despite holding a 3-1 first-leg advantage.
Ancelotti would prefer a less nerve-jangling success this time.
"We're not thinking that it's easy. That's the opposite of what we think. I know this competition well. I know what can happen in football," he said.
"Last year, we thought the second leg would be the most difficult game, and we had the advantage (Real won 3-1 at Stamford Bridge in the first leg). Then what happened, happened. We want to struggle less tomorrow."
Real defender Eder Militao agreed with Ancelotti that his team will need to be at their best.
Chelsea were outclassed in the first leg, with Ben Chilwell's red card in the second half denting their hopes of a shock win.
But Militao knows it is essential to avoid gifting Chelsea a lifeline with careless mistakes.
"Of course, they had some good chances," said Militao. "Thibaut (Courtois) made good saves. They have great players.
"We know we can't miss tomorrow. Who makes the least mistakes will end up winning so we've got to turn up with the same attitude we had in the first leg. Don't overthink it."
