Harlequins director of rugby Conor O'Shea was disappointed as his side lost a thrilling battle before a crowd of 82,000 at Twickenham.
Despite having 75 per cent of possession and playing most of the attacking, Quins could not capitalise and fell to a 30-25 defeat to Northampton Saints.
"There is a huge amount of frustration as we didn't get the breaks. There are loads we have to work on but very little went our way. We gave away a couple of needless penalties and the charge down just after time, which saw them score was crucial." said O'Shea.
Despite these criticisms, Quins showed a huge improvement in their performance as each side scored three tries.
George Lowe, Jack Clifford and replacement Sam Twomey were the Quins scorers with Tim Swiel kicking two penalties and two conversions.
Saints' tries came from Samu Manoa, George North and Kahn Fotuali'i with Stephen Myler's goal-kicking making the difference as he succeeded with three penalties and three conversions.
To run the league leaders so close drew praise from O'Shea, who added: "If we play like that we will beat a lot of sides. I'm happier with that performance as it's a step forward and I believe we've turned a corner.
"We've a long road ahead though to get back up the Premiership table."
Northampton director of rugby Jim Mallinder gave full credit to the efforts of his opponents and said: "We were put under a lot of pressure as Quins played really well.
"They kept their patience and caused us problems when they moved the ball wide but I didn't think we defended particularly well."
Inspired by number eight Samu Manoa, Northampton raised their game in the second half to gain a crucial win.
"In the second half we got a good grip on the game through our set-piece. We didn't play particularly well but when you are away from home, you don't have to play too much rugby to get the result and it was a massive positive for us to get the win." said Mallinder.
Mallinder was also full of praise for man of the match Manoa, adding: "It was a remarkable performance from him and it was a massive boost to us for him to play the full 80 minutes. He's had a virus and has been in bed for the last 24 hours."
Manoa, who scored the opening try before creating the second for North after charging down Swiel's clearance, was at the forefront of a massive defensive effort from his team - but he played down his contribution.
"I back my boys and we back our fitness. Quins played really hard but we had plenty of gas left in the tank," he said.
With this win Northampton remain one point clear of Bath at the top with Mallinder content with the Saints' season to date.
He added: "Bath are playing really well but we are only halfway through the season. However we are where we want to be as it is important that we finish in the top two."