2013 alabama (kick 6 game), though it was replaced by the victor in that game, another sec team (au)
Probably sometime before the 7 consecutive NCs? I know in '94, Alabama's only loss was by 1 point to Florida in the SECCG. Florida's loss @ FSU in '96 was damning at the time. The Gators needed 3 unlikely things to happen to get the rematch (which they did, and won). In 2001, two SEC teams headed for a showdown vs Miami lost out (Florida vs Tennessee, then Tennessee vs LSU in Atlanta). In 2002, Georgia suffered its only loss to Florida in late October, and almost certainly would have been ranked above OSU, with all their unimpressive, close wins.
FYI,
I think the question was in the current CFP era, when a singular loss would have immediately excluded an SEC team. Which isn't the most fair question, because obviously it hasn't kept them out.
2013 was still BCS era, so it was top 2. Bama dropped to 4 in the AP after the Auburn loss, but then moved up to 3 ahead of MSU, who had just beaten then-#2 OSU to win the B1G. So in the CFP era, the loss to Auburn wouldn't have knocked them out.
In 1994, Bama dropped from 3rd to 6th after losing in the SECCG. Florida actually only moved up to 5th, as they were 9-1-1. According to the AP, that would have given us a CFP of Nebraska, Penn St, Miami, and Colorado.
In 1996, Florida only dropped from 2nd to 4th after that FSU loss, and recovered up to 3rd in the final pre-bowl rankings. So in the CFP era, that loss would not have knocked them out of the running. Oh, and of course this was back in the AP beauty pageant days, so despite entering bowl season as the #3 team and there being no BCS, they were put into what basically became the national championship game per the Bowl Alliance, as #2 ASU played in the Rose Bowl instead. So Florida got to rematch FSU and was named national champion after ASU lost in the Rose.
