A year ago, Matthew Nicks' men were among the leading flag contenders as they surged to the minor premiership.
But their campaign unravelled when they lost consecutive home finals while Rankine was out suspended for a homophobic slur.
Now the silky-skilled match-winner is firing on all cylinders, having torched his former club Gold Coast ahead of the fifth-placed Crows' blockbuster clash with Sydney on Friday night.
"He's been huge in the role he's played and he's embraced a team-first, selfless role," Keays told reporters on Monday.
"He's been doing that so well and then you've seen that he can put the cherry on top when he needs to with his amazing ability.
"He'll be so important for us, as will a lot guys going into that (finals) period.
"But since he's got here he's always been a really valued and important part of our squad.
"We're lucky to have him and it was great to see him have such a good game against his former side as well. I'm sure it's always sweet for him to do that."
Adelaide (11-6) have won five of their past six outings, with Keays agreeing the Showdown defeat to Port Adelaide was an aberration in an otherwise strong run of form.
He said maintaining focus will be crucial heading into the business end of the season.
"In this town, we just have to accept that there'll be a bit more noise than other places with teams contending, but that's alright," Keays said.
"That's our job, we just ride that, and try to keep our heads down and focus on the work.
"Any team would prefer to be in that underdog spot, so hopefully we can stay in that mindset and keep that mentality going forward."
Keays expects a finals-like intensity against Sydney (13-4), who lost a top-of-the-table clash with Fremantle last week.
"It's just an exciting challenge to test ourselves against these top teams," Keays said.
"Watching their game against Freo ... it was like a final. The intensity and the way that game was played felt like that was a well.
"I guess we can expect that sort of intensity from Sydney on Friday night, which is super exciting for our group."
Keays was involved in a comical mix-up late in the win over Gold Coast, when miscommunication from the bench led him to hand off a goal to Taylor Walker.
The players believed Walker's next goal would be his 700th AFL major, so Keays gave his teammate the ball for an easy snap.
But it turned out the milestone was still one goal away for Walker, who kicked five on the night.
"We actually went a bit early," Keays said.
"The message came around that he was on 699, and that's the one that I handed off to him, so we celebrated like he got the milestone.
"We didn't know he still had one more to go, so he didn't tell anyone that.
"I think he was happy to accept the handball and kick the goal, so hopefully it's this week."
