The striker tucked away a 13th-minute penalty to ease the pressure after a difficult start at the Cambs Glass Stadium before finshing off Dylan Duncan's break forward to double his tally five minutes before the break.
Luke Berry reduced the arrears for Cambridge, who held the game as a testimonial for their long-serving player Josh Coulson, but we found more space to play as the second period went on and, with captain Luke Amos throwing himself in the way of everything and Christian Maghoma also kept busy at the back, we had the platform to produce some nice stuff going forward.
Harrison quickly restored our two-goal cushion from close range and he, along with lively substitute Kazaiah Sterling, went close a handful of times before Uche Ikpeazu bundled his way through to grab another one for the hosts with virtually the last action of the game, finishing an entertaining affair at 3-2.
We endured a slightly disjointed start as Cambridge showed their Football League savvy on a big pitch to prevent us from getting on the ball and controlling the game but, to our youngsters' credit, we stood up to their threats in the main and ensured that Coulson's early drive, blocked amid a mass of bodies in the area, was their best chance of the first half.
The opening goal on 13 minutes helped to settle us down further. Maghoma, a powerful and vital figure at the back throughout, lofted the ball forward for Joe Pritchard, who controlled at the corner of the box before being tripped by Jake Carroll just inside it. Harrison kept his cool in front of a stand packed with Cambridge fans to send ex-Millwall goalkeeper David Forde the wrong way from the spot.
Above: Joe Pritchard on the ball.
Front man Harrison chipped Forde but saw his effort hit the post midway through the first period and Pritchard saw his shot saved on the counter before we doubled our lead with five minutes to go until the break. Midfielder Duncan robbed Leon Legge centrally and drove through on goal under pressure before squaring for Harrison to roll into the empty net.
The second half was much more open and, although Berry dealt us a blow when he got goal-side of Japhet Tanganga and smashed past Jonathan De Bie seven minutes after the restart, we controlled the play for large spells.
Harrison's third, on 64 minutes, was a back-post tap-in after Jack Roles exchanged passes with Samuel Shashoua in a tight area and got the ball out from under his feet to tee the striker up.
Shilow Tracey and Sterling, twice, were denied a fourth goal through some fine saves but, after the latter's exquisite touch sent Harrison through down the left and the forward's shot was kept out, Ikpeazu latched onto a long ball over the top and clipped it beyond De Bie to give the large home crowd something to cheer in the second minute of stoppage time.
ASSISTANT COACH JUSTIN COCHRANE SAID
"The boys worked really hard. We were playing against an experienced opposition who play quite a direct style of football but I thought we dealt well with long balls, picked up second balls well and imposed our style on them, creating quite a few chances doing that. Players that we have at Tottenham have got to be able to control the game. Players who are under a lot of pressure can still take the ball, still manipulate the ball and play between lines – I think we did that. Luke Amos and Dylan Duncan covered a lot of ground, they gave us a platform to play and Shayon has come up with multiple goals so that's good from him. He's approached training with the right attitude, approached today's game with the right attitude so I'm pleased for him. He's a young man finding his way but he played against experienced centre-halves today and he caused them problems. We're pleased in general to see the boys stand up to the physical test and also win the technical side of the game. It's a notch up from Ebbsfleet last week but today we had a different result and a pleasing outcome."
Cambridge United: Forde, Carroll, Taylor, Legge, Berry, Dunk, Ibehere, Osadebe, O'Neil, Coulson (c), trialist. Substitutes: Deegan, Mingoia, Ikpeazu, Azeez, Roberts, trialist (GK), Amoo, Elito, Davies, Darling, trialist.
Spurs U23s: De Bie, Eyoma (Lock 74), Bennetts, Amos (c, Skipp 79), C Maghoma, Tanganga, Roles (Sterling 70), Pritchard (S Shashoua 46), Harrison, Duncan, Tracey (Loft 70). Substitute (not used): Freeman (GK).
Goals: Cambridge United - Berry 52, Ikpeazu 90+2; Spurs - Harrison 13 (pen), 40, 64.
Referee: Chris Pollard.
We return to Ploufragan, France at the end of next week ahead of our annual participation in the European Under-21 Tournament. We'll face Paris Saint-Germain, EA Guingamp and FC Lorient in Group B, with the competition running between Friday 28 and Sunday 30 July.