Northampton captain Dylan Hartley admitted his side's display against Ulster "was not good enough" after slipping to a 25-6 defeat at Franklin's Gardens.
The Aviva Premiership team became the latest opponent to be beaten by Ulster, who scored four tries to make it 13 successive wins this season.
Saints now know they need to win the reverse fixture at Ravenhill to avoid the prospect of an early exit from this season's Heineken Cup.
"That was not good enough from us," said England international Hartley.
"We speak about intensity, they brought bags of it and we didn't bring enough. They are unbeaten and they showed why. They are a good team but we made them look better than it could have been.
"We had internationals returning, injured players returning and our strongest team on the field but you can't just turn up and expect it to happen and I think that happened tonight. We got showed up by a good team.
"They did exactly what we would like to do to another team. They forced us into errors. It is not good enough."
Hartley's misery could increase if he finds himself in hot water with the disciplinary officials after an off-the-ball clash with Rory Best.
"I don't think it was an incident," the hooker added.
Andrew Trimble and Tommy Bowe crossed in the first half to put the visitors 13-7 before a try from Jared Payne five minutes after the break opened up a comfortable cushion.
And despite flanker Iain Henderson being sin-binned with 10 minutes to go, Ulster grabbed a late bonus point when lock Dan Tuohy dived over in the right corner in the last minute.
"That was a bit of a statement," said coach Mark Anscombe.
"We weren't even thinking about the bonus point. We were more than happy to come here and take the win.
"We are not getting carried away. Northampton have too many quality players and they will bounce back from this performance.
"We have to go out and do it again next week or this will count for nothing."
The only disappointment for the Irish province was captain and second row Johan Muller forced off with what may possible be a broken arm.