The Nigerian international insists the 6-1 UEFA Champions League defeat at the Nou Camp in December still hurts but Celtic haven't let in a goal in four games since that night in Spain and are on a run of six domestic shutouts in a row.
The Hoops haven't conceded in over eight hours of domestic football - including five consecutive league games - and Ambrose says the painful memory of their Champions League defeat is spurring him and his fellow defenders on.
And he said the latest 1-0 win over Inverness Caledonian Thistle on Sunday, when Celtic moved 11 points clear at the top of the Scottish Premiership, highlights the importance of a strong defence especially when the strikers are not in top form.
Building on from Barcelona
"It's important for us not to lose goals. The defence always wants to keep getting better and to keep getting as many clean sheets as we can," Ambrose said. "But we don't count them. You have to go out and do your best every time and in games like this, when you only score one goal, keeping a clean sheet gets you the points.
"We know that if we can keep a clean sheet it is the most important thing because we always feel we can score a goal. Sometimes it is only one but it can be two, three or more. We are just trying to ensure we don't concede goals.
"Since the game against Barcelona it has been in our head that we want to do better in every game. We spoke after the match against Barça but it has gone now and we have put it behind us. We were disappointed with how that game turned out because you never plan for something like that to happen.
"We were up against a team who could do that to anybody but we could have done better. Since then we have worked extra hard to try to do better than we did that night. We have stepped up and defended better."
Next up for Celtic is a clash with Partick Thistle on New Year's Day at Parkhead. The Hoops have gone 18 league games unbeaten and will be huge favourites to make it 19 against the Firhill side who are on a run of nine games without a win.
However, Ambrose is taking nothing for granted ahead of Wednesday's game. "We know it will be tough but we are ready," the Nigerian international said. "We just want to keep winning and trying to keep clean sheets."
Elsewhere on Wednesday, Dundee United will want to end a run of two consecutive defeats when Aberdeen visit Tannadice, Inverness Caledonian Thistle host Ross County in the Highland derby and second place Motherwell welcome St Johnstone to Fir Park.
On Thursday, Hibernian host Hearts in the Edinburgh derby. In-form Hibs have won their past two matches while Hearts have yet to claw back the 15 point deduction they received at the beginning of the season for entering administration.