Cruz vaulted into fourth place in the Hong Kong trainers' championship following the victories of Jack Win, Winning Dragon and Viva Popcorn, with 26-year-old Chung partnering the latter two to match the braces of senior jockeys Zac Purton and Hugh Bowman.
After registering his Hong Kong breakthrough with victory on Winning Dragon in the Class 3 Selkirk Handicap (1650) after earlier prevailing on Viva Popcorn to victory in the first section of the Class 4 Lancashire Handicap (1650m), Chung acknowledged the challenges posed by Happy Valley's circuit's unique turns and contours.
"It feels great (to ride a double). I always struggled a bit at Happy Valley in the first few months. My boss, Mr Cruz, gave me some instruction after that time and helped me improve. It's quite a tricky track, it's still quite difficult for me at this stage but I'm learning as quickly as I can," Chung said.
A dual Hong Kong champion trainer and six-time champion jockey, 66-year-old Cruz trails only John Size (56 wins), Frankie Lor (48), Ricky Yiu (47) in this season's standings as the veteran continues to excel in one of the most competitive racing jurisdictions in the world.
Hong Kong International Sale graduate Nordic Dragon impressed Hugh Bowman with his fourth win in seven starts after the HK$7 million purchase forged to victory in the second section of the Class 3 Wiltshire Handicap (1200m) for Danny Shum.
"The pace was right on tonight, but he had to make up a fair bit of ground on his own and then when I needed him to lift, and I asked him to do so, the response was very good," Bowman said after completing a double, having also successfully partnered Cruz's Jack Win in the Class 5 Hereford Handicap (1200m).
"He's (Nordic Dragon) an improving horse and I guess he'll go up in grade and down in weight, which might make it hard for me, but nevertheless I think he's got more in store."
Purton praised Jamie Richards' handling of talented Hoss after the Fiorente gelding's dogged effort to land the Class 3 St George's Challenge Cup Handicap (1200m).
"Jamie's done a really good job with him," Purton said after the four-year-old made it three wins from five starts over the course and distance. "The horse has also done a really good job.
"He's bred to go further but he's been going so well here at the track and distance that we've left him at it, but tonight might have suggested he might want to go a bit further and we might try that now especially with the extra weight on his back."
Richards said: "He's been running really consistently, he's a horse that's on the way up and he got the job done. There was a little heart flutter there halfway down when that thing poked through, but he's going well."
Richards and Purton also combined with lightly-raced Happy United, who prevailed at his fourth start in the second section of the Class 4 Renfrew Handicap (1200m).
A son of Sweynesse - the sire of champion sprinter Lucky Sweynesse - Happy United was unplaced in his first three attempts but fought on courageously under Purton's urgings in a blanket finish to deny Young Life Forever by a short head with the same margin to Loriz to give Richards a double.
"Things are ticking along well. I think we're going to run out of horses a little bit at the end of the season but we've just got to be patient and wait for the new ones to arrive," said Richards, who improved his tally to 30 wins in his first season.
Me Tsui-trained Fortune President's last-stride victory in the second section of the Class 4 Lancashire Handicap (1650m) - at 46/1 - caught many by surprise, but not Silvestre de Sousa.
"With the light weight (117lb), yes, I thought if I put him behind the leaders, he would go there with an each-way chance," the Brazilian said.
"He just got a bit uncomfortable around the bends, so it was just about balancing him and keeping him interested and his mind on the job and he responded in the straight."
Returning to Happy Valley for the second time this season after victory on Sha Tin's dirt on 26 February, Fortune President found a midfield trail - just as De Sousa envisaged - before pipping Splendid Living by a short head.
A clever ride by Luke Ferraris was pivotal to Ai One's victory in the Class 5 Chester Handicap (1800m) for Jimmy Ting before Antoine Hamelin slotted his 14th win for the season when John Size's A Americ Te Specso swept to victory in the first section of the Class 4 Renfrew Handicap (1200m).
"He (A Americ Te Specso) was a nice chance, one of the favourites and when you have the favourite on your hands, it makes your life easier. We had a good draw, everything went smoothly and on the home turn, I just had to come out and ask him and my horse responded really well. He fought to the end, so that's nice," the Frenchman said.
Hong Kong racing continues at Sha Tin on Sunday (7 May) with the G3 Queen Mother Memorial Cup Handicap (2400m).
