Nemanja Matic revealed Serbia had waited for the Republic of Ireland to commit men to attack before pressing for what proved the deciding goal at the Aviva Stadium on Tuesday night.
The sides were deadlocked at the break but Alexander Kolarov's brilliantly finished effort in the 54th minute proved enough for a 1-0 victory.
"We knew that we would have some space to play because they had to try to win and to take risks," the Manchester United midfielder told RTÉ Sport.
"We had more space to play in the second half than in the first because they attacked a little bit more.
"We used that chance and Kolarov scored an amazing goal."
Thumping finish from Kolarov after smart pass by Kostic. 1-0 to Serbia #IrlSer #RTEsoccer pic.twitter.com/BQ3RtAbJtY
— RTÉ Soccer (@RTEsoccer) September 5, 2017
Matic was delighted with how Serbia resisted Irish efforts to find an equaliser, even after going to ten man following Nikola Maksimovic's professional foul on Daryl Murphy.
Serbia now lead Group D by four points from Wales and victory in their next game against Austria or final match against Moldova will guarantee their place at World Cup 2018.
"We did well in a stadium which is very hard to play in, against a good team," he said.
"It was hard for us, especially in the last 10 or 15 minutes when we had 10 men and they put on an extra striker or two. They pressed us and we showed character.
"We're now really close to qualifying. There are still two games to play and we have to win the next game to be sure.
"We have five points more than the Republic of Ireland with two games, which is a lot but we have to concentrate."
His captain Branislav Ivanovic said it was among the toughest games he's played for Serbia.
"It was probably the most difficult game in my career with the national team," said the former Chelsea defender.
"We didn't play to our level all game but we showed what we needed to do to win the game.
"We are so proud. We showed a lot of character under a lot of pressure.
"It's our biggest win in qualification and now we're waiting for the last step."
