This used to be a much more common thing back in the days when a loss here and there didn’t derail a career … or even stand as a major setback. I have a couple of examples to start it off: Pipino Cuevas lost a 10-round decision to Andy “Hawk” Price and six weeks later destroyed Angel Espada to become WBA welterweight champion. Jersey Joe Walcott lost two in a row — to Rex Layne and Ezzard Charles (and not in a remotely close fight) — but the (mob) powers that be were determined to keep giving him chances til he won, and he beat Ezz in a rematch to become heavyweight king. I know there are others. Let’s see if we can compile a good list.
Jorge Lujan - lost a 10 rounder to Jose Cervantes before stopping Alfonso Zamora for the bantamweight title.
Just thought of 2 more. Denny Moyer lost a split decision to Emile Griffith before winning the vacant jr. middleweight title against Joey Giambra. Also, and ironically, Ralph Dupas lost a tight one to Sugar Ray Robinson before winning the jr. middleweight title from the same Denny Moyer. In the case of Dupas, I wouldn't have a problem with it because it was well publicized that he deserved the decision against Robinson, so he got his title shot anyway.
Are we including champs who lost their title, and then regained it in an immediate rematch (in which case the list will be quite enormous)? Or should we restrict the names to those who won their first title fight, coming off a defeat?
Not exactly what you’re looking for but Eusebio Pedroza got knocked out twice in a row and then won his first world title four fights later and didn’t lose the title for 7 years.
The sequence which remains constantly at the forefront of my mind (I probably think about it most every other day since Billy Petrolle is one of my guys) is Tony Canzoneri's one-round kayo of Al Singer to win the world lightweight title just after he had lost a decision to Petrolle.
Sung-jun Kim lost an OBPF light flyweight title fight to countryman Sang-il Jung. This earned him a world title fight against Netrnoi Vorasingh, which Kim won with a dramatic knockout in the third. Marlon Starling was knocked out cold in the fight before he beat Lloyd Honeyghan. Does that count?
Sonny Liston qualifies. After his loss to Marshall in 1954, Liston went on a 28 fight win streak until 1964 and again in 1965 both times losing against Ali. Then Liston went on another 14 fight win streak. For the sake of the conversation I left out the Phantom punch and all the evidence that Liston most likely threw both fights against Ali.