After coming within a couple of metres of becoming the first team to record a bonus point win in Glasgow in seven years, the Saints instead found themselves on the end of a Peter Horne sucker punch which snatched both the points and a European knockout place.
"It was really disappointing," Mallinder told BBC Radio Northampton. "We came here with the intention to win and to get four tries for the bonus point and we got very close. We created quite a lot of opportunities, especially in the first half, but we're loose in other areas of our play, and when you're loose in the Heineken Cup you often lose.
"I thought that the bench did well and gave us energy and we created more opportunities, but it wasn't to be.
"Credit to Glasgow, they stuck at it and we gave them those opportunities. We gifted them a turnover from which they scored, and at the end some ill discipline let us down.
"It's been very frustrating and a mixed competition for us. We've had three good wins, but then we've had three losses as well. We want to compete at the top and getting into the further stages in Europe, and we've got to better."
Saints set out their stall early, sending several kickable penalties to the corner in search of early tries. But Glasgow showed why they are currently second in the Pro 12 by holding out until Dom Waldouck dived between the uprights after 31 minutes, and then by scoring two tries themselves in the second half, firstly through man of the match Niko Matawalu and then Horne's late effort.
"Early on from a captain's perspective I could have gone for the sticks to try and secure the win, but we backed ourselves and it didn't quite pay off," Hartley told BBC Radio Northampton. "Hindsight makes me wonder if I should have gone for the points early doors, but I've got to live with that.
"We didn't start well in either half. They got their tales up and you've got to remember that they were a team with nothing to lose. They wanted to spoil our party and they certainly did.
"They're a good team; we found that out at home when they scored three tries in 20 minutes. That day we dug in and came back, but testament to them today they played the full 80 and it came off for them.
"Come Monday morning we'll deal with what hand we're dealt, and if that means we're focusing on the Aviva Premiership and LV= Cup then that's what we'll do."
Attention next week switches to the LV= Cup, in which the Saints lie top of their pool and where a win over Gloucester could mean a third semi-final in four seasons.
"Having the internationals away means that some of the other lads will have the chance to step up," Mallinder added. "We'll be focusing now on the LV= Cup and the Aviva Premiership, and they're two competitions that we've still got a chance in, and we've got to put every effort into doing well in those."
As with every home game the support from the stands could make the difference, and you can get behind the Saints by booking your tickets.