Steve Bruce's side had to play with 10 men for more than an hour after the dismissal, for an apparent head-butt, but held out well against a Canaries side that looked lacklustre.
The win was a big relief to Sagbo, who had performed a classic hero-to-villain vignette just a few minutes after winning the penalty that Robbie Brady slotted home for the only goal of the match.
Hull will be buoyed by the three points, and the impact of former Tottenham duo Tom Huddlestone and Jake Livermore making their first starts in central midfield.
Scoring goals will no doubt be the issue for the Tigers in the future - Bruce makes no secret that that is going to be his side's chief challenge, for despite finishing second in the Championship last season the Tigers scored five fewer goals than relegated Peterborough.
Considering that statistic, it was no surprise to see Norwich being the more adventurous side in the early stages and Leroy Fer, who was suspended for the opening match of the campaign, putting in a prodigious leap at the far post to meet Steven Whittaker's cross. It looks as though his header was in, but Hull goalkeeper Allan McGregor was relieved to see it miss the upright.
With goals set to be hard to come by, McGregor looks to be an important signing in turns of keeping them out, and he pulled off a full-length diving save to deny Nathan Redmond.
But just as it looked as though it was going to be the Canaries dominating events, Hull began to show some attacking spirit.
The tricky Sone Aluko pulled off a deft backheel which wrong-footed the Norwich defence and left Slovenian skipper Robert Koren clear on goal - but he scooped over and a golden opportunity had gone begging.
The first key event of the match arrived with 20 minutes gone, when former Tiger Michael Turner was penalised for a shove on Sagbo as the forward attempted to reach a deep cross.
Source: PA
Source: PA