The American has been one of the busiest players on the ATP Tour this season but he has taken his foot off the gas since the US Open, appearing in only the Laver Cup and Shanghai Masters.

He beat Britain's Cameron Norrie 6-4, 6-3 to kick off the defence of his Tokyo title and said it was "probably an advantage that I might be less burnt-out".

"After the US Open, I think I had played the most matches of anyone on tour," said Fritz, the number one seed in Tokyo.

"I thought it made sense to start the Asia swing in Shanghai. I feel motivated and ready to play."

World number 10 Fritz beat fellow American Frances Tiafoe in last year's Japan Open final and has won six career titles.

He is the highest-ranked American in the world and overcame an early setback to dispatch Norrie in his Tokyo opener.

"I was holding easily and then out of nowhere he broke me, so it was a tough spot to be in," said Fritz.

"I feel like I played a couple of really good points to break and I played the bigger, more important points better in the return games.

"I definitely upped my level."

Fritz was joined in the next round by countryman Ben Shelton, who beat Japan's Taro Daniel 3-6, 6-4, 7-6 (7/2).

US Open semi-finalist Shelton struggled with his serve in the first set and had to dig deep to recover in the second.

He said the experience of going to a third-set tiebreaker in his previous two matches helped him get over the line against home favourite Daniel.

"Being able to be in that situation time and time again has definitely prepared me for that moment," said Shelton, who has risen to number 19 in the world.

"When it came up today, I wasn't too nervous because I knew I'd been there before and that gave me the confidence to play the style that I wanted to play in the tiebreaker."

Number two seed Casper Ruud of Norway beat Japan's Yosuke Watanuki 7-6 (8/6), 6-3 to reach the second round.

Australia's number four seed Alex de Minaur also progressed with a 4-6, 7-6 (7/4), 7-6 (7/1) win over Britain's Jack Draper.

Australia's Alexei Popyrin eliminated Russian number seven seed Karen Khachanov 6-4, 6-2.