Ablett trailed Selwood by two votes heading into the final round, before polling three votes while rivals Selwood and Dane Swan failed to poll.
The Gold Coast captain finished on 28 votes, one vote ahead of Selwood with Swan another vote further back on 26.
10.29pm: The 2013 Brownlow Medal looms as a race in three with Joel Selwood and Dane Swan narrowly trailing leader Gary Ablett after 20 rounds.
Ablett has 25 votes, the fast-finishing Selwood has 24 and Swan, who also enjoyed a strong finish to the season, has 23.
Dan Hannebery has also polled well to date with 21 votes but the Sydney Swans struggled to the line in the home and away season and Hannebery's form dipped accordingly.
Ineligible Cat Steve Johnson lies fifth with 20 votes as a reward for an consistently excellent year.
10.15pm: Gary Ablett remains the leader of the 2013 Brownlow Medal after 17 rounds, three votes ahead of Sydney Swan Dan Hannebery and six votes clear of a group of three more stars.
Ablett has 24 votes with six rounds to come and Hannebery has 21, while Joel Selwood, Dane Swan and Patrick Dangerfield are on 18.
Highly-fancied Hawk Sam Mitchell is 10 votes behind Ablett on 14 votes, but he is predicted to finish strongly.
9.58pm: Patrick Dangerfield has joined Gary Ablett and Dan Hannebery at the top of the leaderboard in the 2013 Brownlow Medal after 15 rounds.
Ablett still leads with 20 votes, with Dangerfield and Hannebery two votes behind on 18 votes.
However, Collingwood dynamo Dane Swan has mounted a charge to sit fourth on 16 votes.
9.27pm: Sydney Swans midfielder Daniel Hannebery has thrown down an early challenge to Brownlow Medal favourite Gary Ablett, trailing the Gold Coast skipper by just two votes at round 12.
Hannebery streaked to an early lead before the star Sun racked up 16 votes in six rounds from rounds seven to 12 for a total of 20 votes. It equals the record vote tally after 12 rounds that was previously recorded by Jobe Watson and Simon Black.
Joel Selwood, widely considered Ablett's main rival for this year's Brownlow, has 11 votes after 12 rounds to sit equal sixth with five other players.