Andreas Weimann notched City's third from close range when latching onto a low near-post cross from the right in the 66th minute.

The winning margin would have been bigger but for some fine Shea saves as Luton plunged to their eighth successive away league defeat.

City could have been five up at the interval, making a mockery of the pressure being exerted on head coach Lee Johnson by a section of fans after a run of four losses.

Diedhiou should have done better when heading wide from a Weimann cross in the 16th minute and Shea had to produce a spectacular diving save to keep out Josh Brownhill's 25-yard curler nine minutes later.

The Luton keeper did equally well to smother a Watkins downward header in the 36th minute after another Eliasson cross to the far post.

Brownhill fired over from a 30-yard free-kick with the visitors almost exclusively on the back foot. Their only first-half threat was a 19th-minute header from Matt Pearson from a LuaLua cross that went well wide.

Eliasson, who has been racking up assists in the Championship this season, was a constant threat on the left flank for City and Diedhiou's spot-kick was just reward for his side's dominance.

Luton boss Graeme Jones made a change for the second half, sending on Martin Cranie for right-back Luke Bolton, who had been given a tough time by Eliasson.

It quickly made a difference and Hunt had to clear off the line when City keeper Dan Bentley could only take the pace off a Harry Cornick shot.

Pelly-Ruddock Mpanzu sent a curling effort from distance inches wide with Luton enjoying their best spell of the match.

But City still carried a threat and Shea saved a Diedhiou header from Brownhill's chip into the box before Weimann's goal put the result beyond doubt.

The strike took any remaining stuffing out of Luton, who might have conceded more when pushing extra men forward in the closing stages.

There were few moments of anxiety for Bentley, who was well protected by the central defensive combination of Ashley Williams and Tomas Kalas. But City are likely to face a tougher test at home to Brentford on New Year's Day.