A day after heavy rainfall caused play to be suspended, Britain's Katie Boulter returned to clinch a 6-3 6-1 victory at the Japan Open over wildcard Himeno Sakatsume.

The world No 58 concluded a dominant victory in one hour and 32 minutes in Osaka, and she will next face Swiss player Viktorija Golubic for a place in the quarter-finals.

The victory gives Boulter a 20-20 record across her last 40 matches, and a confidence boost following a period in which she has only played three matches since September 30, owing to early exits at the China Open (second round) and Wuhan Open (first round).

On Monday, the match between Boulter and Sakatsume had barely started when the players were forced off court after torrential rain arrived in Osaka. Given the venue didn't have a roof, the court was open to all of the elements.

By that point, only three games had been played in the first set, with Sakatsume leading 2-1 at the time of the suspension.

Play was resumed, but another rain delay followed with the score 6-3 3-1 (40-30) to Boulter, meaning both players had to leave court and return on Tuesday to finish the contest.

When play restarted again, 30-year-old Boulter continued to dominate, winning seven of her eight service games overall and claiming five of nine break point chances.

Swiatek withdraws from Ningbo Open with left thigh injury

Elsewhere, Iga Swiatek has withdrawn from the Ningbo Open in China because of an injured left thigh, diminishing her chances of contesting the season-ending WTA Finals at Indian Wells next month.

The six-time major winner lost to eventual champion Maja Chwalinska in the semi-finals at the Wuhan Open last week and struggled at times in that match.

"After careful consideration, I've decided to withdraw from the tournament," Swiatek said in a statement posted on social media Tuesday by the Ningbo tournament. "I've been experiencing an ongoing problem with my left thigh over the past weeks and I feel that giving myself the time to rest and recover is the right decision."

Swiatek was one of three players in contention for the last spot in the eight-player field for the WTA Finals with Karolina Muchova and Marta Kostyuk ahead of tournaments this week.

The WTA, in a preview of the Ningbo tournament, said if Swiatek didn't reach the quarter-finals and Kostyuk doesn't reach the final here, Muchova will secure the remaining spot for the season-ending tournament at Indian Wells starting November 8.