Nadir Ciftci scored a double to secure vengeance for himself and Dundee United as Jackie McNamara's side stormed into the William Hill Scottish Cup semi-finals with a 5-0 thrashing of nine-man Inverness.

Ciftci was sent off in a stormy League Cup quarter-final defeat at the Tulloch Caledonian Stadium in October but he had a far happier trip to the Highlands this time as he sent United on their way to the last four when he twice took advantage of poor defending in the first half-hour.

Caley Thistle ended the first half three goals and a man down following Gavin Gunning's penalty, and goals from Gary Mackay-Steven and Stuart Armstrong made it an emphatic fifth consecutive win for United.

The hosts had both Greg Tansey and Marley Watkins sent off for studs-up challenges on Paul Paton as they suffered a second successive 5-0 drubbing with just seven days remaining until their League Cup final against Aberdeen.

Ciftci had his red card for a clash with Graeme Shinnie rescinded following his previous visit but he still had a nervous and lengthy wait for the full consequences of that confrontation before eventually receiving an immediate one-match ban for pushing assistant referee Gavin Harris, who was running the line again on Sunday.

And he looked determined to enjoy this occasion, trying his luck twice from long range before opening the scoring in the 15th minute following John Rankin's lofted through-ball.

All but Josh Meekings of the Inverness back four kept a high line as Ciftci ran forward but the centre-back looked to have the situation under control before Dean Brill came racing off his line. Ciftci got to the ball first, nodded it past the goalkeeper and finished from a tight angle as Meekings crashed into the post in an unsuccessful attempt to clear.

Billy McKay nodded over following a set-piece after recovering from a reckless but unpunished challenge from Paton and United went two up in the 27th minute.

Sean Dillon put Inverness on the back foot when he launched a clearance from the edge of his own six-yard box as United defended several phases of a corner. Meekings' passback was slightly short as it bobbled on the rutted goalmouth but Brill made the clearance despite Ciftci's pressure. However, the ball bounced off Meekings and into the path of the United forward, who tapped home from two yards.

Gunning leathered home a 36th-minute penalty after winning the spot-kick when he ran across Shinnie as the defender attempted to clear Rankin's forward pass.

And Caley Thistle's day soon got worse after Tansey went into a challenge for a bouncing ball with his studs showing. The midfielder did not make a lunge but Paton's foot caught the studs as he cleared the ball and he screamed in agony before referee Willie Collum immediately showed the red card.

Shinnie had long-range strikes beaten away either side of the interval but any comeback hopes they had were extinguished in a 49th-minute counter-attack when Mackay-Steven finished brilliantly after Armstrong had released him from inside his own half.

Armstrong put his own name on the scoresheet eight minutes later when he got across Gary Warren to powerfully head home Keith Watson's cross.

And Collum showed another red in the 71st minute when Watkins slid in with his studs showing, despite playing the ball.

Caley Thistle's only consolation is that both Watkins and Tansey will be available for next Sunday's Celtic Park final thanks to their Scottish Premiership match against Hibernian on Wednesday. They will miss that game as well as their team's next Scottish Cup match.