As widely predicted, Olazabal handed wild cards to Colsaerts and Ian Poulter - a star of the last two matches - for the defence of the trophy in Chicago on September 28-30.
The 29-year-old from Brussels, winner of the Volvo World Match Play in May, becomes the only rookie in a side containing eight of the Celtic Manor heroes.
They are Poulter, Rory McIlroy, Luke Donald, Lee Westwood, match-winner Graeme McDowell, Francesco Molinari, Peter Hanson and Martin Kaymer, while Justin Rose and Sergio Garcia are back from the 2008 line-up and 43-year-old Paul Lawrie earns his second cap a remarkable 13 years after his first.
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On selecting Europe's biggest hitter for a Medinah course where length could be a huge asset Olazabal said: "We do have a huge amount of experience on that team and I don't think it's a gamble.
"I think the guy has shown a lot of heart, a lot of character.
"Obviously we know that the Ryder Cup atmosphere is very different to any regular event, even major events - but I think he's got the game, and to be honest, the desire and the determination of being there has been huge."
Colsaerts played eight of the last nine weeks of the qualifying race. That included seeking an invite to the Wyndham Championship in America and finishing seventh there now appears as important for him as winning was for Sergio Garcia.
"His match play record is very good and don't be mistaken - he does a lot of other things as well as hitting the ball a long way," added Olazabal.
"He's had a very solid season and on top of that he's made the extra effort trying to make the team.
"He really showed me that he wants to be a part of that team. Those are the reasons for me to pick him."
Olazabal telephoned Harrington - winner of only two of his last 13 cup games - in America and also spoke to USPGA runner-up David Lynn and Spaniards Rafa Cabrera Bello, Gonzalo Fernandez Castano and Alvaro Quiros to let them know they were not going to be picked.
On Harrington, with whom he had a public spat in 2003 after he thought his integrity was questioned, Europe's captain said: "I was very straight to the point.
"I know he tried hard. He played well at The Masters (eighth), he had a good US Open, but he was 19th on the list.
"I know he's a great player. I would have loved to have him on the team the same way I would have loved to have Paul Casey, Robert Karlsson, Henrik Stenson.
"Those are great players, but you need to be playing good, simple as that. I think he took it well and that was it."
Annoyed that the Seve Trophy incident was brought up in print last week, Olazabal admitted that the call to Harrington was the hardest to make.
"I felt I needed to make that call more to him that anybody else," he said.
"When I said last week he needed 'at least a win' I was meaning that if he was to win I would think about him. It would make life more difficult."
Contacting Poulter was a much more pleasurable experience obviously - and there has rarely been a more obvious pick. He has won seven of his last eight cup games.
"His attitude and his spirit in the Ryder Cup team has always been great," added Olazabal. "He's one of those players that likes to be in that situation.
"The two times I had the opportunity to share a few moments with him at Valhalla and Celtic Manor you didn't need to motivate him.
"Just by looking at his eyes (you knew) he would give everything that he had during that week. That's Ian."
From his Florida home Poulter commented: "I was actually thrilled to get the call. It was a great moment and I'm going to be thrilled to again pour some passion over the holes at Medinah."
Asked what Colsaerts would feel like on the first tee Poulter replied: "I'm not sure if you can put it into words to be honest. I think Nicolas will feel the excitement that everybody and anybody that has played Ryder Cup has ever felt before.
"That is a lot of intense pressure, a lot of excitement and I think Nicolas is going to do an incredible job handling that and delivering with the rest of the guys on the team."
There was one other call Olazabal made - to Kaymer, who has not had a top-10 finish since April and who was the subject of rumours that he might pull out.
Kaymer issued a statement saying he was working hard and promised "I will be ready", while Olazabal's mind went back to 1993.
"I was struggling big-time. I called Seve (Ballesteros) and said 'anybody can play better than I am at the moment and I'm thinking of not going'.
"It's a good job it was on the phone. He would have smashed my face."
They won two more games together at The Belfry, making it 11 wins, two halves and only two defeats together in their cup careers.