Dundee dropped to fourth in the Championship table as they fell to a 2-0 defeat to Inverness at Dens Park.
First-half goals from Aaron Doran and James Keatings did the damage as John Robertson’s Caley Jags strengthened their grip on second spot.
Ayr winning at Dunfermline meant the Dark Blues dropped to the fourth and final promotion play-off spot, 20 points behind leaders Dundee United.
Dee boss James McPake stuck with the same line-up which earned a point in the Dundee derby with 17-year-old Fin Robertson starting in the middle of the park after a terrific display at Tannadice.
Inverness were the first to threaten but Nikolay Todorov could only head Miles Storey’s cross over the bar after three minutes.
Caley skipper Carl Tremarco went closer on nine minutes as he got on the end of another Storey cross after a period of pressure. However, Dark Blues keeper Jack Hamilton gathered the header comfortably.
Hamilton then made a smart stop from a whipped Keatings free-kick minutes later as the visitors continued to push for the opener.
On 16 minutes Charlie Trafford forced a routine save out of Hamilton before, just a minute later, Inverness got the goal their play deserved.
In acres of space down the right, full-back Shaun Rooney had the freedom of Dens Park to pick out Doran in the centre of the box and the Irish attacker duly lashed home from 15 yards.
On 24 minutes, ICT were two to the good. From their own corner, Dundee compounded to lose possession and allowed the Highlanders to break.
Former Dundee United man Keatings led the charge and finished the counter attack off himself, coolly slotting beyond a helpless Hamilton in the home goal.
The Dark Blues huffed and puffed for the remainder of a dismal first half for them but were unable to lay a glove on Inverness as the boos rang out among the sizeable home support on the half-time whistle.
Four minutes into the second period, Dundee forced Mark Ridgers into his first save of the afternoon as the ICT goalie stooped to turn Jordan Marshall’s long-range effort behind for a corner.
Jordan McGhee was next to test Ridgers, firing in a dipping effort just before the hour mark, but the Caley stopper was able to gather.
Moments later, Paul McGowan’s header from a deep Sean Mackie cross forced Ridgers to tip over as the Dee sought a way back into the contest.
On 70 minutes, Kane Hemmings laid in Marshall but the left-back saw his effort from 16 yards deflected behind.
Inverness’ front four continued to look threatening but, largely, the Dee defence kept them quiet in the second 45.
However, McPake’s men were unable to carve a way through an organised ICT defence with the rookie boss cutting a frustrated and under-pressure figure throughout.
With Ayr and Dunfermline to face next, Dundee will certainly need to perform a lot better if they are to stay in the mix for the promotion play-offs come the end of the season.
Dundee XI (4-4-2): Hamilton (GK); Kerr, Meekings (C), McGhee, Marshall; Robertson, Dorrans, McGowan, Mackie (Todd 62); Johnson (Cunningham 85), Hemmings.
Subs not used: Ferrie (GK), Forster, Byrne, Moore and Cameron.
Inverness XI (4-2-3-1): Ridgers (GK); Rooney, Donaldson, McHattie, Tremarco (C); Trafford (Carson 56), Vincent; Storey (McKay 45); Keatings Doran; Todorov (White 72).
Subs not used: Mackay (GK), McCart, Curry and MacGregor.
Referee: Don Robertson.