Ajayi did not score in Rotherham’s 2-0 loss to Sheffield United in their last encounter but scored two in their 3-2 home win against Blackburn Rovers.
The Nigerian international was given a starting berth by Paul Warne for the game against QPR at Loftus Road.
The first half ended goalless but it was Semi who scored the game’s opener in the 71st minute.
Bright Osayi-Samuel a player of Nigerian descent gave QPR a lifeline when he converted a ball through to him by Nahki Wells in the 85th minute to level the scores.
Semi would have the final say when he converted a corner by Anthony Forde in the 90th minute.
With just few minutes left to play Semi and his Rotherham teammates held on to claim all three points.
Before the game against QPR, Rotherham had not recorded an away win in the Championship this season.
Semi who is a defender has been flourishing in a midfield role which has seen him score four goals in four games.
The win helps Rotherham in their push to move up in the Championship as they aim to avoid relegation.
Semi is expected to return to action when Rotherham host Norwich City in their next encounter scheduled for Saturday, March 16.