Rohan Ricketts started the ball rolling with a fine opener in what was always an entertaining encounter at Kettering Town's Rockingham Road.
We had the better of it in terms of possession, especially in the second half, but had to defend resolutely when Foxes had their best spell just before the break.
In that time they pulled a goal back, Rob Burch was forced into a double save and Spase Dilevski cleared off the line.
Burch produced another fine save on the hour mark but otherwise it was a half we dominated and game we deserved to win - no other conclusion looked likely after Defendi drilled home our third goal on 64 minutes.
Both sides had threatened before Ricketts opened the scoring after 14 minutes.
Dilevski found him in the box, his fake to shoot with his left foot completely sold Adam Wykes before he lashed home with his right from 12 yards.
It was soon 2-0 as the home side failed to clear Reto Ziegler's corner, Dean Marney hammered the ball across goal and Barnard was on the spot to nod home from close range. The striker looked lively all night.
Barnard might have added to his tally but appeared brought down as he was about to shoot six yards out after 35 minutes - no penalty was awarded and Leicester hit back three minutes later.
Tomi Petrescu slid home Louis Dodds' cross to make it 2-1 and we had to be on our mettle in City's best spell, Burch produced a double save to deny Dawson from distance and Dodds from close range before Dilevski headed Butcher's volley off the line.
Apart from one Burch save to turn Petrescu's volley aside on the hour, the second half was all about us.
We got ourselves into three or four decent positions before and after that Burch save before Defendi finally restored the two-goal cushion. Barnard was involved again, this time spreading the ball wide to Marney, he picked out Hughes whose low cross was drilled home by the Brazilian.
We saved the best until last. With 77 minutes on the clock, Ziegler spotted Barnard's run between Leicester's central defence, hit him with the perfect 40-yard crossfield pass that Barnard controlled and slotted superbly home.
MINUTE BY MINUTE
1min: Marney rifled early shot over from 30 yards.
3mins: Butcher run into box, pulled back to Petrescu but Kelly there to make superb block.
5mins: PENALTY? Appeals for handball waved away as Defendi's header hit a defender.
11mins: Burch out quickly to gather as Petrescu went after Butcher's pass.
14mins: GOAL. Dilevski pass into Ricketts, faked to shoot with left foot which sent Wykes sprawling before lashing home with right from 12 yards. 1-0.
19mins: GOAL. Leicester failed to clear Ziegler's corner, Marney hammered back across goal from byline and Barnard nodded home from close range. 2-0.
20mins: Ziegler 30-yard run before shooting wide from edge of box.
25mins: Ambitious effort from Norval from fully 40 yards, Burch had to watch closely, dipped a yard wide.
30mins: Decent build up by City, ball worked to Dawson in box, shot high and wide under pressure from O'Donoghue.
33mins: Marney screamer from 25 yards dipped just over.
35mins: PENALTY? Barnard went down under Norval's challenge as he was about to pull the trigger just six yards out, nothing given.
38mins: GOAL. Dodds break down the right flank, into box, cut back from byline, Petrescu got a yard in front of Kelly and rammed home on the slide from close range. 1-2.
41mins: DOUBLE SAVE. Dawson given too much room 30 yards out, took it on five yards before shooting low to Burch's right, decent save to palm out but then up quickly to deny Dodds on rebound.
42mins: OFF LINE. Dilevski nodded away after Butcher met Wesolowski's corner on full volley.
43mins: Burch comfortable save as Norval tried his luck from 30 yards.
Half-time: Leicester City 1, Spurs 2
49mins: Burch did well to hold tricky, dipping volley from Dawson.
53mins: Silva Sousa break into box but opted to shoot when should have squared to unmarked Barnard.
54mins: Barnard powerful volley looked goalbound until hit Elliott.
54mins: Marney shot from 16 yards deflected into side-netting.
60mins: SAVE. Burch fine reactions to turn aside Petrescu's volley from 10yards.
61mins: Barnard blasted wide after Silva Sousa won possession off Wykes.
63mins: Marney fierce drive from 30 yards almst deceived Logan who did well to turn aside.
64mins: GOAL. Barnard kept possession well from corner, spread play to Marney, he dinked ball to far post where Hughes crossed for Defendi to drive home from 10 yards. 3-1.
77mins: GOAL. Superb goal. Ziegler spotted Barnard pulling away from markers from left touchline, fired the perfect pass fully 40 yards that Barnard took on his chest before guiding home from a tight angle. 4-1.
Line-ups: Leicester City: Logan, Canero, Wykes, Elliott, Norval, Dawson, Gondal, Butcher, Dodds, Petrescu (Muggleton, 77), Wesolowski. Subs: Austin, McClymont, McKay.
Spurs: Burch, Kelly, O'Donoghue, Defendi, Ziegler (Mills, 77), Hughes, Marney, Ricketts, Dilevski, Silva Sousa (O'Hara, 64), Barnard. Subs: Fulop, O'Hara, Mills, Barcham, Malcolm.
Lee Barnard struck his third and fourth goals in three games and Rodrigo Defendi his first for the club as our reserves beat Leicester City on Monday night.