The north Londoners struggled to break down Steve Bruce's men, who threatened from set-pieces, until the former Valencia stepped up to bury his third spot-kick of the season
Referee Michael Oliver pointed to the spot when Jan Vertonghen's cross smashed into the arm of Ahmed Elmohamady, though it looked unintentional, with Soldado stepping up to slot away the spot-kick and earn Spurs their first home win since September.
Andre Villas-Boas made one change to the Tottenham side that won at Aston Villa in their last Premier League outing, with Gylfi Sigurdsson dropping to the bench as Aaron Lennon started.
|VIEW FROM WHITE HART LANE
|By Greg Stobart
Hull manager Steve Bruce waited for referee Michael Oliver by the tunnel and you can understand his frustration after his side were denied a point by the penalty decision 10 minutes before full-time.
Tottenham appeared to have run out of ideas before Oliver pointed to the spot after the ball Ahmed Elmohamady’s hand - via his foot - after Jan Vertonghen had struck the ball from barely two yards away.
Roberto Soldado made no mistake from 12 yards to take Spurs up to fourth place, three points behind leaders Arsenal, but it was yet another stuttering home display from Andre Villas-Boas’ side.
They seem to lack the creativity to break down teams who look to sit deep at White Hart Lane and, as the frustration grew in the stands, the players became increasingly nervous and indecisive.
On-loan Hull midfielder Jake Livermore was ineligible to face his parent club, but Tom Huddlestone lined up against his former employers.
Brazilian midfielder Paulinho had the first clear-cut chance of a frantic first half after 10 minutes when he got on the end of Lewis Holtby's dangerous free kick but narrowly cleared Harper's bar from close range.
Harper was called into action five minutes later when in-form winger Andros Townsend tried his luck from 20 yards, but the Hull keeper got down to palm the ball away.
The visitors showed attacking intent of their own and striker Yannick Sagbo burst into the penalty area before forcing a save out of Hugo Lloris.
Hull appealed for a penalty when Paul McShane tangled with Kyle Walker 22 minutes in, but referee Oliver saw nothing untoward.
Huddlestone almost ended his long goal drought in spectacular fashion when volleying just over the bar from 20 yards, while Walker's venomous drive was palmed away by Harper at the other end.
Villas-Boas replaced Sandro with Mousa Dembele at the break and Soldado had his first sight of goal nine minutes into the second half when Towsend played him in, Harper making a fine save at full stretch to deny the former Valencia striker.
After further dogged resistance from Hull, Tottenham were then awarded a penalty when Vertonghen's cross struck Elmohamady's arm and Oliver pointed to the spot, much to the anger of Steve Bruce on the sidelines.
Soldado stepped up to casually send Harper the wrong way and lift the tension at White Hart Lane, his third goal from the penalty spot this season.
There was concern late on for Townsend, though, when he went over the advertising boards at full tilt, but he was able to return and Spurs survived a late scare when Huddlestone blasted a free kick wide in the closing seconds as Tottenham moved up to fourth place.