Brickies take the points at Woodstock ParkA baffling second half slump saw Whyteleafe surrender what was to prove a very brief mid-match tenure of top-spot in Bostick League Division One South.
Leafe started the game brightest with an early Ross Elsom strike from 25 yards narrowly over keeper Daren Hawkes's crossbar.
In the 8th minute spritely Leafe forward Daniel Ajakaiye, returning to the starting line-up following a frustrating early season injury, was fouled on the edge of the area. Tommy Hutchings sweetly curled the resultant free kick into the left-hand corner of the net.
On 16 minutes powerful midfielder Olumide Oluwatimilehin almost doubled the visitors' lead, his shot from 20 yards just inches wide of Hawkes's left-hand post.
Sittingbourne began to rally, forcing a 20th-minute corner, one of many that would test the Leafe defense all afternoon. On this occasion Kane Rowland met the inswinging ball at the far post forcing alert keeper Matte Pierson to smartly tip it over his crossbar.
Moments later Pierson was relieved to see a speculative Tom Loynes shot fizz narrowly wide of the upright.
Just before the half-hour mark Ajakaiye and Lanre Azeez combined well on the right, each having strikes on goal blocked by a crowded defence.
The game continued to flow from end to end, although with few clear-cut goalscoring chances. The hosts were frustrated on 41 minutes when a credible penalty appeal after Loynes was flattened in the area was waved away by referee Mr Evans.
At the break Whyteleafe were still temporarily sat at the top of the league table and were clearly seeking to sustain such a lofty position. It was not to be.
Sittingbourne immediately showed their second half intent, the impressive Loynes delivering a perfect cross from the left, met by a Bola Dawodu volley that flew just wide of Pierson's left-hand upright.
On 61 minutes it was Loynes again delivering from the left, a low cross tapped home by Rowland from close range to level the scoreline.
Whyteleafe's fine recent form and style deserted them, relying instead on long clearances from Pierson or the defence that were lapped up, in particular by giant centre-half Lex Allan, putting Leafe immediately on the back foot again time after time.
The winning goal came in the 71st minute when the increasingly impressive Loynes found himself in space 25 yards from goal and struck an unstoppable curling shot past the startled Pierson.
With the visitors offering very little by way of attack, Bourne were left to comfortably hold onto their lead and claim the three points, leaping up to second place in the table, ahead of Leafe in fourth.
Despite a lackluster second-half display by the latter, a playoff meeting at the end of the long season ahead would not be entirely surprising, given both clubs' similar ambitions and strong starts to the campaign.
Whyteleafe: Pierson, Adesida, Musungu, Oluwatimilehin, Howlett-Mundle, Forbes (Scarborough 46'), Azeez (Clement-Peter 63'), Elsom, Ajakaiye, Hutchings (Postance 76'), Amoo. Subs not used: Treagus, Nkori-Vencelas