Millwall 0 Northampton 1

But Jackett was upbeat about his side's second half performance, even though their cup ambitions were scuppered for another year.

He said: "There's a lot there. It's a frustration that we didn't convert the chances we created or really capitalise on some good wide play. We got good crosses into the box and did threaten them, without a doubt.

"When you lose games it's frustrating. Results count, because they build confidence for the players and supporters.

"But in our two defeats we've not been outplayed or been second best but we have to start better at home, there's no doubt about that. We dominated for an hour today and it was long enough but we have to start quicker, with a better tempo and more aggressively."

He was certainly right about the need to start better as his side looked sluggish and short of ideas in the opening stages last night. They paid the price when Jason Crowe got across Andy Frampton to slot home after 16 minutes to give Northampton the lead.

The warning signs came as early as the first minute when Ryan Gilligan almost put the visitors ahead but wasted a good opportunity from close range.

A subdued atmosphere and a small crowd at The Den didn't help, with the game at times feeling more like a pre-season warm-up than a full-blooded cup-tie.

The Lions began to come back into matters after 35 minutes when a neat exchange of passes gave Lewis Grabben a shooting opportunity from the edge of the box but the young winger pulled his shot wide of Mark Bunn's right-hand post.

Jackett made a couple of changes at half-time, bringing on big striker Tresor Kandol for his home debut and introducing some guile in the form of Ahmet Brkovic.

Both substitutes seemed to perk Millwall up and they began to press for an equaliser. Kandol should have done better with a couple of clear headed chances but somehow contrived to put them both wide, while Grabben was unlucky to see his speculative 30-yard effort bounce off the wrong side of the upright.

Northampton grew in reliance on their heavyweight centre-forward Adebayo Akinfenwa, who had a spell on loan at The Den last season, but the visitors offered very little else in the second half.

Kandol took a heavy knock as he challenged for a ball right at the death and required lengthy treatment, but even with four minutes of added time it wasn't to be Millwall's night and the stands were all but empty by the time referee Clive Penton blew for full-time.

Jackett was clearly annoyed at the defeat, particularly following hot on the heels of last Saturday's 4-3 reverse at Oldham.

"It is a blow," he said. "Nobody likes losing, least of all me. It definitely hurts.

"I didn't think we started the game very well, with enough tempo about us. We're looking to do better than that. I felt the last 15 minutes of the first half and the second half we dominated, had all the ball and all the chances. But you need to put those chances away and we didn't.

"It was a frustrating evening but other positives were Hackett coming into the side after a long injury. I don't think he's played since last September for Millwall and, playing at right-back where I've got both [Danny] Senda and [Marcus] Bignot unavailable, he did well and I'm pleased with his performance."

The Lions have the chance to get their season going when they meet Southend at The Den on Saturday afternoon.

Millwall: Forde, Frampton, Whitbread, Alexander (Kandol, 46), Grabban, Hackett, Craig, Martin, Fuseini, Laird, Abdou (Brkovic, 46). Unused subs: Edwards, Dunne, Harris, Smith, Forbes.

Booked: Frampton, Hackett.

Northampton: Bunn, Crowe, Jackman, Hughes, Gyepes, Doig, Constantine (Holt, 76), Akinfenwa, Davis, Gilligan (Osman, 59), Guttridge (Coke, 59). Unused subs: Larkin, Henderson, Dunn, Dolman.

Booked: Doig, Guttridge, Bunn

Attendance: 3,525