UFC on ESPN: Nicolau vs. Perez

UFC on ESPN: Nicolau vs. Perez (also known as UFC on ESPN 55 and UFC Vegas 91) was a mixed martial arts event produced by the Ultimate Fighting Championship that took place on April 27, 2024, at the UFC Apex facility, in Enterprise, Nevada, part of the Las Vegas Metropolitan Area, United States.

Background
A flyweight rematch between former Rizin Bantamweight Champion Manel Kape and Matheus Nicolau was expected to headline the event. The pairing previously met at UFC Fight Night: Edwards vs. Muhammad in March 2021 which Nicolau won by controversial split decision. Their second meeting was previously scheduled for UFC Fight Night: Ankalaev vs. Walker 2 in January 2024 but Kape missed weight and the bout was subsequently cancelled. In turn, Kape pulled out due to a rib injury and was replaced by former UFC Flyweight Championship challenger Alex Perez.

A lightweight bout between Road to UFC Season 1 lightweight winner Anshul Jubli and Maheshate Hayisaer was scheduled for this event. However, Jubli pulled out due to unknown reasons and was replaced by Gabriel Benítez.

A lightweight bout between James Llontop and Lando Vannata was scheduled for this event. However, Vannata pulled out for unknown reasons and was replaced by Gabriel Green. Green was also withdrew from the bout for unknown reasons and he was replaced by newcomer Chris Padilla.

Joel Álvarez and Mateusz Rębecki were expected to meet in a lightweight bout. However, Álvarez pulled out due to undisclosed reasons. Rębecki instead faced Carlos Diego Ferreira at UFC on ESPN: Lewis vs. Nascimento on May 11.

At the weigh-ins, James Llontop and David Onama missed weight. Llontop weighed in at 156.5 pounds, half a pound over the lightweight non-title fight limit. Onama weighed in at 148.5 pounds, two and a half pounds over the featherweight non-title fight limit. Both bouts proceeded at catchweight with both fighters forfeiting 20% of their purses, which went to their opponents Chris Padilla and Jonathan Pearce, respectively.

Bonus awards
The following fighters received $50,000 bonuses.
 * Fight of the Night: No bonus awarded.
 * Performance of the Night: Alex Perez, Bogdan Guskov, Jhonata Diniz, and Uroš Medić

Aftermath
As the starting ring announcer Joe Martinez became ill during the event, UFC's roving reporter Charly Arnolt replaced him briefly and became the first female ring annoucer in the promotion's history.