Comebacks were the central theme of a rain-affected second day at the 2019 ITF Junior Finals as a quartet of players recovered from earlier losses to revive their chances of progressing to the tournament's knockout phase.

It promises to be an intriguing and exciting final day of group-stage action on Friday as the qualification puzzles in all four pools remain far from solved. 

As heavy downpours battered Chengdu on Thursday, play was initially transferred to the Sichuan International Tennis Centre's covered courts before being forced completely indoors as the deluge continued.

USA’s Hurricane Tyra Black was the first opening-day loser to prosper in the new surroundings, beating home favourite Zheng Qinwen, while junior world No. 1 Jonas Forejtek, Argentina's Thiago Agustin Tirante and Elsa Jacquemot of France followed suit and boosted their hopes of a semi-final spot. 

Impressive in defeat against newly-installed girls' world No. 1 Diane Parry on Wednesday, Black appeared intent on bouncing back in style as she clinically dispatched Zheng 6-2 6-2.

Black, who claims to be inflexible off court but "stretchy woman on it", revealed post-match that there had been a degree of soul-searching overnight.

"For the whole night I was so upset that I didn't really think about this match, but when I woke up this morning I was completely focused on doing whatever I needed to do on the court," Black told itftennis.com.

"I really wanted to win more than anything and get myself back into contention. I have lost to her previously so was a little nervous to be playing her. To win in straight sets is really exciting for me."

With Parry chalking up a commanding 6-2 6-1 victory over Japan's Natsumi Kawaguchi - her second success of the tournament - she has one foot in the last four, while Black and Zheng have a win apiece. Parry plays Zheng in the final Group Li match, while Black does battle with Kawaguchi.

Forejtek, meanwhile, stormed back into contention for the semi-finals by beating Chinese wild card Yunchaokete Bu, who was forced to retire after falling awkwardly and incurring an apparent ankle injury with proceedings locked at one set all.

The Czech, who triumphed at last month's US Open Junior Tennis Championship, was subdued in defeat against Harold Mayot on Wednesday and relieved to kickstart his ITF Junior Finals campaign.

"I was so annoyed [after defeat to Mayot]. In a different tournament I would have been out by now so I need to take the chance I have," said Forejtek. "I did not start the tournament well so hopefully after this I will be a bit more with the game.

"I played much better. The balls are flying here - it's so different to other tournaments. I need to improve."

Forejtek is likely to have to navigate a heavyweight tussle against Denmark's Holger Vitus Nodskov Rune - a clash involving two of the top three-ranked boys on the planet - if he has designs on lifting silverware in the Far East. 

Rune claimed a second success in as many days by edging an incredibly tight and edgy encounter against Mayot, prevailing 7-6(5) 7-6(6) in the final battle of the day. 

Tirante, meanwhile, was another player to rekindle hopes of progressing to the competition's latter stages after completing a straight-sets triumph over Canada's Liam Draxl, who remains winless.

He now faces a titanic winner-takes-all clash with Japan's Shintaro Mochizuki on Friday after the reigning Wimbledon boys' champion succumbed to the recurring theme of Thursday fightbacks.

Mochizuki was a set to the good before Valentin Royer rose from the ashes to post a 2-6 7-5 6-1 victory. Royer, who is ranked 10 places lower than junior world No. 2 Mochizuki in the latest boys' standings, is now the outright leader in Group Yong following back-to-back victories. Tirante and Mochizuki have one success apiece. 

"I played Shintaro a couple of months ago [at JA Milan in May] and beat him so I have confidence," said Tirante. "After losing yesterday, I just kept saying 'give yourself a chance to win this trophy'. 

"I played well today and hit the ball true. It was so important to win. Winning means I still have a chance to lift the trophy."

The qualification picture remains just as nail-biting in Group Liang as Jacquemot recovered from her loss to Daria Snigur and thrashed an out-of-sorts Kamilla Bartone of Latvia 6-1 6-4. 

Bartone now faces a tough assignment against Wimbledon girls' champion Snigur, who prevailed 6-4 6-7(1) 6-1 against Russia's Oksana Selekhmeteva, on Friday. Jacquemot, who like Bartone has one victory to her name, will go head-to-head with Selekhmeteva.