"I was fairly flat. I practised a lot," Tomic said.
"I'm never going to be the fittest player on the tour.
"I'm [196cm] and I have to rely on different things like my serve and today I served terrible.
"But I lost to a top player, one of the best of the last six or seven years," said Tomic.
Meanwhile, another controversial Australian, Nick Kyrgios, overcame a minor basketball injury to open his year with a crushing 6-3 6-4 win over Spain's Feliciano Lopez at the Hopman Cup in Perth.
Kyrgios entered the match with strapping just below his left knee after taking a tumble while playing basketball a few days earlier.
The world No13 brushed off the discomfort to put Lopez to the sword in a match that lasted 65 minutes.
Kyrgios powered down 14 aces for the match, and raced through the first set in just 23 minutes.
The 21-year-old was surprised at how well he'd played given he had reduced his on-court practice time during the off-season, and instead focused on boosting his fitness.
"I felt like I was going to be a bit rusty at times.
"But I played really well today," Kyrgios said.
"It's surprising because I haven't been doing much on the court.
"I've just been trying to get into a good head space and be ready.
"I was really happy with the level today."