Town were once more left ruing the lack of a killer instinct in front of goal, as lowly Rocester executed the perfect smash and grab manoeuvre with a winner two minutes into added-on time.
Prior to the late decider, the hosts had twice equalised strikes from the Staffordshire outfit, but there was no opportunity to do so again after away skipper Martin Smyth lashed home at the death.
Rugby’s starting line-up showed four changes from the midweek cup win at Wulfrunians, with Aiden Print and Craig Kelly restored as full-backs, David Kolodynski fit to return up-front and Ben Ashby preferred to Josh Ruff in midfield.
However there was a disastrous and controversial start to the game for Valley, when Rob Ritchie-Smith lifted the ball into the net after Niall Cooper’s ineffectual punch to Eric Graves’s centre – with the home players looking for the game to be stopped for treatment to the injured James Dance.
After this first minute setback, Rugby were soon on the front foot though, with Fabian Smith putting a free-kick over the bar and Ruben Wiggins-Thomas heading Kolodynski’s cross straight at Richard Froggatt.
Harry Holloway was on the end of another Kolodynski cross, but his header flew over the frame, with Kolodynski himself then also firing one off-target from the edge of the penalty area.
Town finally levelled things up after Froggatt had saved three efforts from Kolodynski in quick succession, only to see the final parry fall at the feet of Smith – who duly fired the ball home.
The visitors responded well though, and Cooper turned Harry Lansdowne’s shot round the post shortly before their lead was restored when the unmarked Tom Brown scored from a James Frost corner.
Wiggins-Thomas missed a great opportunity to even things up again before the interval after Froggatt spilled the ball, but the Rugby striker could not provide the necessary finish.
Both Tevin Shakespeare and Kolodynski sent strikes too high in the early stages of the second period, with Wiggins-Thomas then helping another good chance over the bar.
At the other end, Cooper then did well to deny Smyth after he had broken clear of the Valley defence.
Wiggins-Thomas had headed Holloway’s cross over, before he finally found the target on 64 minutes when he showed good composure to stroke the ball past Froggatt after Print’s long searching pass had picked him out.
Froggatt pulled out a decent save to keep out substitute Ruff’s strike and Holloway headed one onto the roof of the net, although the visitors nearly scored themselves after Cooper’s error let in Oliver Roome – but he could only find the side netting.
Valley’s final chance of a winner came when Print’s cross lacked quality with a number of team mates waiting in good positions, and Rocester then made the hosts pay when Smyth powered home Callum Riddell’s flick on to a searching set-piece delivery.
Line-up: Cooper; Print, Kelly, Dance, Castleton; Smith, Ashby (Brathwaite), Holloway (Thornton); Shakespeare (Ruff), Wiggins-Thomas, Kolodynski. Subs not used: Hall, Harris. Booked: Ashby.