York, who led by two points going into Saturday's fixtures, were frustrated by a stubborn rearguard action from Sheffield Collegiate, while Castleford picked up maximum points at home to Sheffield United.
It leaves the teams tied on points with just two matches remaining.
Castleford are without Shaun Le Roux (pictured) and Charles Finan for both matches. Le Roux is in Amsterdam and Chicago to fulfil his professional squash obligations and Finan is returning to Bristol for his medical studies.
And with club professional David Wainwright also likely to be on Yorkshire duty, Cas will need to be at their best to pip York to the title.
Put into bat, Castleford rallied after a poor start to Saturday's game at Savile Park. They were 26-3 until David Wainwright and Chavez Younes steadied the ship. Younes was unlucky to be adjudged leg before for a patient 23 but Wainwright went on to hit an excellent 63 from 82 deliveries.
And with Shaun Le Roux (39 from number eight) and Will Hodson (18 not out) playing superbly at the end of the innings, Cas were delighted to reach 206-8 at the close.
Sheffield never seriously threatened the total, despite useful knocks from Neil Armstrong, Matt Milburn and captain Neil Longhurst.
Yorkshire all-rounder Wainwright was the pick of the attack with 3-29 as the visitors crumbled to 127 all out. Sheffield were hampered by the loss of top order batsman Andy Hurst, who was unable to bat after colliding with a team-mate in the field during Castleford's innings.
Meanwhile, club captain John Randerson has slammed the decision to replay Castleford's Yorkshire League KO Cup final with York on September 20.
Only 28 overs of last Sunday's showdown were possible. York were 120-2 when the game was washed-out by heavy rain.
York play Scarborough on Sunday and compete in the Black Sheep Champion of Champions Trophy Final the following Sunday (September 14).
September 20 looks like the first available date, confirmed an angry Randerson: "Much to my disappointment, the league president has ruled that York's Black Sheep fixture takes priority of the Yorkshire League Final.
"We will be without key players on this date, including David Murphy, who will have returned to Australia, and Chris Young, who is also going to play club cricket in Australia.
"York will be in the same boat but to me it makes a mockery of the competition when both teams will be forced to field sub-standard teams in the supposed showpiece event of the season."
Castleford visit third-place Rotherham on Saturday before ending the league season with a home match against Yorkshire Academy. York travel to Scarborough on Sunday and close with a visit from Sheffield United.