Dimitrov starts the year ranked third, having won his biggest title in November when he triumphed at the ATP Tour Finals at the O2 Arena in London.
Germany's Zverev won five titles in 2017, including two Masters 1000 titles, finishing the year just behind Dimitrov as the world number four.
Besides world number one Rafael Nadal and defending champion Roger Federer, Dimitrov and Zverev are considered genuine title threats.
However, Bulgarian Dimitrov, a semi-finalist in Melbourne 12 months ago, is trying not to get ahead of himself.
"Until it's done, I don't want to have any (sixth) sense, to be honest," the Bulgarian told reporters in Melbourne on Saturday.
"Obviously I've achieved certain things that I've always wanted to. I always wanted to be a top-five player. I did it. I wanted to win a Masters 1000 event and I did it. I haven't dreamt that much about winning at the O2, but I did it."
Dimitrov admitted it was a different feeling to see himself as the third seed in a grand slam event, but that the hard work was still to be done.
"It doesn't mean anything," he said. "Of course, I'm pretty happy and excited with what I have achieved. Obviously, I have high expectations of myself. I want to do the best that I can."
GRAND SLAM DISAPPOINTMENT
Zverev emerged from the pack in 2017 with his five titles, including Masters 1000 victories at Rome and Montreal.
The only thing lacking from the German's list of honours is success at the grand slams, having only made it to the last 16 just once, at Wimbledon last summer.
"I think improving the grand slam performances is one thing (he needs)," he said.
"The furthest I've got was to the fourth round of Wimbledon. A lot of times not because I played bad, but because I played very good opponents.
"I lost to Nadal here. I lost to (Milos) Raonic in Wimbledon. Every time in five sets. That's nothing to worry about too much. But obviously that's one goal for me this year."
Zverev, who is now coached by former world number one Juan Carlos Ferrero, said he had no doubts about his ability.
"I've showed on multiple occasions over the year that I can play and beat the best guys in the world," he said.
"I mean, I'm number four in the world for a reason. Not trying to sound cocky or anything, but I've always said that I've always been working hard physically, I'm always trying to improve the performance at the grand slams.
"Hopefully I can do so this week."
(Reporting by Simon Cambers; Editing by John O'Brien)
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