News of the replacement broke via UFC president Dana White's Twitter account Tuesday afternoon.
"Get ready [Philadelphia] for Rashad Evans vs. Tito Ortiz," White wrote.
Ortiz also confirmed the matchup to ESPN.com.
"Rashad is a great opponent. I've got my hands full," Ortiz said. "It's going to be a challenge, but I'm taking it in full stride and making the best of it. My emotions right now are to get into the gym and start training again."
Evans told ESPN.com's Franklin McNeil that he feels good about the fight, despite the sudden change.
"Through the whole process I never lost motivation or focus," Evans said Wednesday. "I didn't dwell on it too long. I figured the UFC would figure something out."
The announcement came hours after multiple reports stated both Ortiz and Lyoto Machida had turned down offers from the UFC to replace Davis. Ortiz confirmed those reports on his personal Twitter account before eventually changing his mind.
"Yesterday they offered the fight. I had just got back from Vegas and was home spending time with my family. I was caught off-guard," Ortiz explained to ESPN.com. "Dana asked if I wanted to fight I said, 'No, not really.' I've got a lot going on with my clothing brand, Punishment.
"Honestly, the biggest difference for me and why I took the fight was my commitment to the UFC -- showing them I'm there when they need me. We've gone through some stuff but we fixed it and I'm there for them."
Ortiz (16-8-1) is just 11 days removed from a first-round submission win over Ryan Bader at UFC 132, a result that saved the 36-year-old's job. Leading up to the fight, White made it clear Ortiz needed a win to continue his UFC career, having dropped four of his last five.
"[Dana] was very happy about it," Ortiz said. "He told me, 'This is going to be a great moment for you. Ride this. Be a champion again.'"
Evans (15-1-1), meanwhile, is likely happy to simply have a fight planned. The former light heavyweight champion hasn't fought since earning a decision win over Quinton Jackson in May 2010.
"Getting back in the Octagon is the thing I am most happy about," Evans told McNeil. "At the same time, I'm thankful that Tito decided to accept this fight and put it all on the line.
Crowned the No. 1 contender following that fight, Evans was scheduled to face then-champion Mauricio Rua at UFC 128 last March but was forced off the card due to injury. He was then set to face current champ Jon Jones, however that fight was scrapped due to an injury to Jones' thumb.
The August bout will be a rematch of a controversial draw between the two at UFC 73 in July 2007. Ortiz was penalized for grabbing the fence in the fight, which ultimately prevented him from taking a decision.
"Having a chance to fight Tito again, it feels like Christmas," Evans told McNeil.
Brett Okamoto covers mixed martial arts for ESPN.com. Information from ESPN.com's Franklin McNeil contributed to this report.