Poulter was handed a 3 and 2 defeat by Thongchai Jaidee on the Gary Player-designed Thracian Cliffs course in the first major tournament held in Bulgaria.
''I got off to a good start with birdies on the first three holes, and it was then a combination of a couple of mistakes and handing Thongchai too many holes,'' Poulter said.
Poulter will face unseeded Thomas Aiken in his final round-robin encounter and will be hoping Jaidee loses to Aiken in the afternoon to advance to the final 16.
Colsaerts, the defending champion, was never in front against Branden Grace, with the South African winning 4 and 3.
''I missed a couple of putts that had I holed would have made my day a lot easier and bring myself into the match,'' Colsaerts said. ''So when you miss those putts, the gap between Branden and myself just got bigger and bigger.''
Graeme McDowell – the highest ranked player in the field at No. 8 – defeated Chris Wood 5 and 3.
McDowell, who lost to Colsaerts in last year's final, was 3 up after eight holes and closed by winning the 13th, 14th and 15th holes.
''I played solidly, and it was important to get off to a nice start but then for the guys that lost today, it's not the end of the world,'' said McDowell. ''They can still go out and try to win tomorrow.''
McDowell will play Stephen Gallacher on Friday afternoon, while Wood will face Gallacher in the morning.