A combination of poor marking and indiscipline was the root of the problem in a game which ended as a contest after 30 minutes.
Rovers Cassidy almost opened the scoring in the first minute when he got on the end of a long Chiedu throw in from the right wing with his header skimming the top of the bar.
The visitors took the lead in the 6th minute when Rovers defence allowed Thorniewood’s right winger to cut in and run across the length of the 18yd line unchallenged and lay the ball off to the striker who fired the ball home from close range.
Rovers responded positively and should have equalised in the 10th minute when Grierson crossed from the right resulting in another Cassidy header crashing off the bar from close range.
Thorniewood went two ahead after 25 minutes when Rovers failed to match their opponents slick off the ball movement in front of goal and a clever but simple one two on the left edge of the box cut Rovers defence wide open allowing their striker to side foot the ball low into the bottom right corner of the net.
From the restart a Lafferty run and cross from the left wing found Cassidy on the penalty spot who angled a right foot shot which looked netbound only from the keeper to dive full stretch and palm the ball round his left hand post.
The visitors went three up on 30 minutes following a double deflection of edge of the box shots as the ball looped over Dave Cherries head into the net.
Cassidy hit the woodwork for the third time in the 40th minute as he jinked his way into the box to unleash a powerful shot only to see it cannon off the bar.
Any chance of a Rovers recovery disappear into the ether in the 55th minute when McKenna received a straight red card for verbally abusing the referee.
Rovers worked hard to salvage some respectability from their second half efforts and in the 75th minute a Weir free kick was spilled by the keeper with Chedu firing over the bar from 5yds which summed up the whole match from a Rovers perspective.Match Report by Ian McKnight