Northampton slipped to second place on 30 points, four points off the leaders Exeter who they face next in the competition.
Bristol (pictured, Charles Piutau) gained a share of third place with Sale, on 26 points, one point ahead of Bath.
Lam was disappointed with his side's effort, marred by a high number of turnovers before they got their act together to come home late to claim the win.
Lam said: "We got the result we wanted but not the performance. It was a horrific game. At halftime I said, 'Guys we've just got to flush this one down the toilet' because you can't play rugby with 18 turnovers.
"We just couldn't fire a shot because we kept losing the ball," he said.
They had started the second half well and could easily have scored a try but they turned the ball over again.
The experienced hands in the side had worked them through their problems.
"I said to them 'the purple patch will come' and we had a 10-minute spell of really good rugby but besides that we'll move on from that, it wasn't the best one for us," he said.
"We have our standards and that wasn't good enough for us. You beat Exeter away, you beat Northampton away, the boys can be really proud of that but we've got to get back and tidy up. We can't afford to lose ball from simple turnovers, it makes the game tough," he said.
The incentive to improve was immediate as they next face Worcester. They shouldn't need any incentive to perform against them as they had beaten Bristol well when they were on their own patch last year and they would need to prepare well.
"If we don't the same thing could happen again," he said.
Boyd was disappointed with the way Northampton yielded their advantage.
"At 14-0 I thought things were looking pretty good, but we dropped off a couple of tackles that cost us points and they got their nose in front. We were unable to peg it back in the end.
"We controlled the game for long periods of time, but they scored more points than us so it's very disappointing to surrender that lead here at the Gardens and lose our second game in a row.
"There's work to do.
"We'll have to look at this game again, but it's probably individual errors. Maybe we started running out of puff and the guys we brought on didn't bring the energy we needed.
"At 14-0 at home with 30 minutes to go, we should have been able to close that game out," he said.