McGregor (18-2) has opened as a minus-180 favorite over Aldo (25-1), who is listed at plus-150. A title unification bout between the two is expected to take place either late this year or in early 2016.
The line was set by Nick Kalikas of MMAOddsbreaker.com, who said it was a combination of McGregor's performance against Mendes and the support he received from bettors that made him a clear favorite.
"McGregor answered several important questions, displaying both a terrific chin and a resilient spirit when facing adversity for the first time in his UFC career, despite entering the fight amidst rumors of an injured knee," Kalikas said. "At this point, I have to open Conor near a 2-to-1 favorite. The line might seem a bit high, but make no mistake, the books will need Aldo when it's all said and done."
Aldo was supposed to fight McGregor at UFC 189 on Saturday but withdrew due to a rib injury. Initial betting lines for that fight pegged Aldo, a seven-time defending champion, as a minus-210 favorite.
McGregor support was so strong at the sportsbooks, however, that by the time Aldo withdrew from the fight, McGregor had moved to a slight favorite.