Edinburgh fought back from 10-0 down to ruin Ulster's new stand opening at Ravenhill in the Magners League on Friday, winning 16-13.
Ulster established an early lead through tries from Stephen Ferris and Clinton Schifcofske, but two missed penalties from Humphreys and a yellow card for his replacement Paddy Wallace allowed Andy Moffat's side claw their way back to claim the points.
Tim Visser crossed for Edinburgh on the half-hour before Chris Paterson kicked two second-half penalties and then Phil Godman's drop goal put the visitors ahead with five minutes of normal time remaining.
It had started so differently for the home side. Ferris' return for his first game since suffering a knee injury on the British & Irish Lions' tour seemed to have the desired effect and Ulster's hunger, after last week's surprise win at the Ospreys, was only too evident in their aggressive tackling and willingness to move the ball at pace.
With Edinburgh finding themselves pinned in their own territory, a breakthrough seemed inevitable and both Ferris and Simon Danielli, Ulster's two most dynamic players in the early stages, played a central part in the opening score.
Danielli broke through Edinburgh's defensive line and, when the ball was recycled, Ferris bludgeoned over for the 15th-minute score which Humphreys failed to convert.
Five minutes later, Schifcofske crossed in the left corner for an unconverted try after a break from Darren Cave.
However, the home side then had to absorb some real pressure for the first time in the game and were unable to do so as winger Tim Visser barged over on the left after half an hour.
Paterson added the extras with a great strike from the touchline to narrow Ulster's lead to five points but Humphreys was on target five minutes later with a penalty.
For all their dominance, Ulster should have been further ahead than 13-7 at the break and in the half's final play Humphreys was again wide with what seemed another kickable penalty.
Humphreys may have suffered for his inaccuracy as he was hauled ashore for Wallace to make his first appearance of the season.
But, with Willie Faloon causing mayhem up front, Wallace was wide with a close-in drop goal effort.
Ulster encountered further difficulty just after the hour mark after again failing to convert pressure into points when Wallace was sent to the bin for a professional foul in tackling an Edinburgh player from an offside position.
Paterson added the three points and Ulster's lead was cut to 13-10 and then, seven minutes later, Ulster were penalised at a ruck following a defensive lineout. Paterson made no mistake to draw the sides level.
But even with Wallace back on the pitch, the Scots grabbed the lead with a 75th-minute drop goal from Godman and the remainder of the game was scrappily played out mostly in Ulster's half.
Tries: Ferris, Schifcofske
Pens: Paterson 2
Drop goal: Godman
Yellow card: Wallace (60, Ulster)
Ulster: 15 Clinton Schifcofske, 14 Timoci Nagusa, 13 Darren Cave, 12 Ian Whitten, 11 Simon Danielli, 10 Ian Humphreys, 9 Isaac Boss, 8 Chris Henry, 7 Willie Faloon, 6 Stephen Ferris, 5 Ed O'Donoghue, 4 Neil McComb, 3 Brendon Botha, 2 Andy Kyriacou, 1 Bryan Young.
Replacements: 16 Nigel Brady, 17 Declan Fitzpatrick, 18 Tamiati Horua, 19 Robbie Diack, 20 Cillian Willis, 21 Paddy Wallace, 22 Andrew Trimble.
Edinburgh: 15 Chris Paterson, 14 Mark Robertson, 13 Ben Cairns, 12 John Houston, 11 Tim Visser, 10 Phil Godman, 9 Greig Laidlaw, 8 Allister Hogg (capt), 7 Roddy Grant, 6 Alan MacDonald, 5 Scott MacLeod, 4 Craig Hamilton, 3 Geoff Cross, 2 Ross Ford, 1 Kyle Traynor.
Replacements: 16 Andrew Kelly, 17 Allan Jacobsen, 18 Steve Turnbull, 19 Scott Newlands, 20 Mike Blair, 21 Steve Jones, 22 Nick De Luca.
Referee: Nigel Owens (Wales)
Assistant referees: David Keane (Ireland), Ken Beggs (Ireland)
Assessor: Jack Young (Ireland)
Television match official: Jonathan Peak (Ireland)