Market Harborough were replaced as Midlands Two East (South) leaders by Luton as they lost their unbeaten record to their Bedfordshire rivals.
The match ended 29-25 although Harborough did show their fighting spirit to claw back a losing bonus point.
It started well when Luton received an early yellow card.
But, though they may have been down to 14 men, they attacked and, from a set-piece, the Luton scrum-half found a huge gap in the Harborough defence to run in a try that with the conversion gave the visitors a 7-0 lead.
Harborough fought back and reduced the deficit with a penalty by Callum Blair but Luton restored their lead with a penalty of their own.
This became 10-6 through another Blair penalty but Harborough were clearly not firing on all cylinders.
What followed was difficult to watch as Luton caught the ball in the line and went through a gaping hole to touch down.
The 17-6 scoreline became 22-6 as a simple catch at the front of the line once again demonstrated Harborough’s defensive frailties.
They needed to regroup at half-time and this they did. Harborough dominated the second half.
Michael Woodford touched down and with a Blair conversion it reduced the deficit to 22-13.
The penalty count against Harborough then cost them as Luton kicked to the corner and from the resulting lineout their big forwards set up a series of drives to secure their bonus-point try and a 29-13 lead.
There was plenty of time left in the game and Harborough stormed back with Ed Sumpter using his strength, height and reach to touch down for a try converted by Blair.
Luton were now on the back foot as Harborough started to run the ball from deep.
Joe Margetts, playing his first game of the season, was showing some sparkling touches but it was Ed Parker’s speed that stood out as he raced clear only to see the ball slip from his grasp over the line as he was tackled.
Harborough still attacked and the Luton pack was struggling in the tight.
Despite conceding penalties at the scrum there was no penalty try and, as the Luton scrum broke up, Harborough drove over with Woodford touching down.
However, he was deemed to have run into his own man – a cruel blow as the scrum went to Luton and they cleared their lines.
Fraser Harrop did get a score which closed the gap to 29-25 but there was no time for Harborough to go for a famous win.
The loss drops them to fourth in the league as other results went against them.
That said, only three points separate the top four teams in what is a very competitive league.
Coach Richard Bowden said: “It was an extremely disappointing defeat in a game that we could, and maybe should, have won.
“But we will learn from this game and make it right.”