Spalding United’s under-21s struck eight times for the second successive away game.
The Tulips boosted their goal difference with a fourth win out of five to remain on top of the Lincolnshire FA Under-21 Development League south section.
Spalding took control with goals by Lewis Millington and Jordan Neil but Luke Bristow pulled one back for Harrowby United.
Daniel Moulds made it 3-1 and Layton Maddison added Spalding’s fourth goal early in the second half.
Harrowby United went down to 10 men as substitute Luke Papworth was sent off for a professional foul on Millington.
Another goal for Millington was followed by efforts from Jonny Lockie, Levi Butland and Jordan Heeley.
Our aim is being unbeaten to win the section and go into the grand final.Lewis Thorogood
Manager Lewis Thorogood said: “We can only play what is front of us but I was really pleased overall.
“We carved them open with our width and firepower – simple as that.
“We shouldn’t have given away a goal because we got sloppy and complacent.
“At half-time it should have been 4-1 or 5-1 so we needed that fourth goal at the start of the second half to make it more comfortable.
“Now we need to push on with two home wins before the festive break.
“Our aim is being unbeaten to win the section and go into the grand final.
“I was pleased with the attitude as the boys kept going with a winning mentality to score more goals.
“When we went 4-1 up at home to Sleaford Sports, we started knocking it around like an exhibition game.
“This was a job well done on a very cold night.”
4-5-1: Jessop; Waby, Curry (sub Papworth 50 mins), Bristow, Hopkinson; Wroughton, Evans (sub Clamp h-t), Wood (sub McGowan 73 mins), Jackson (sub Carr 56 mins), McCartney; Smith (sub Clarke 73 mins).
4-2-3-1: Smith; Gordon (sub Heeley 68 mins), Moulds, Fixter, Floyd; Maddison (sub Buckley 76 mins), Clarke; Millington (sub Butland 73 mins), Neil (sub Britton 76 mins), Chipamaunga (sub Couzens 60 mins); Lockie.
Millington (21 mins, 0-1); Neil (25 mins, 0-2); Bristow (27 mins, 1-2); Moulds (31 mins, 1-3); Maddison (47 mins, 1-4); Millington (73 mins, 1-5); Lockie (82 mins, 1-6); Butland (86 mins, 1-7); Heeley (90 mins, 1-8).
Papworth (professional foul).
Grantham Town (H) – Tuesday, November 28.