Ng, in only his second season as a trainer, has led this season's standings since 5 November and held a commanding 16-win buffer on 1 January but his former mentor Lui has since reduced the margin to three – 58 wins to 55 – with 16 meetings left in the season.
Ricky Yiu (47 wins), Tony Cruz (44), John Size (44), David Hayes (43), Danny Shum (43) and Caspar Fownes (43) are also vying for a top-three position.
"As I predicted early in the season, I was expecting them to come hard at me and Francis has - and now we're just trying to manage as many winners as we can," Ng, 40, said.
"From having 41 winners last season to now 58 this season is a big improvement, I think, and at the end of this season, I'll be sitting down to think about what I can learn from this season so we can have a better season next season.
"I'm hoping we can get more winners this season first."
Ng will saddle eight runners this weekend with Taj Dragon (133lb) to face only five rivals in the HK$3.72 million Racing Heritage Handicap – Healthy Happy (135lb), Packing Treadmill (123lb), Atullibigeal (122lb), Wonder Kit (115lb) and Supreme Lucky (115lb).
To be ridden by apprentice Ellis Wong, Taj Dragon will jump from barrier 3 in his first appearance since finishing sixth to Beauty Eternal in the G1 FWD Champions Mile (1600m) on 28 April.
"Dropping back in grade plus the apprentice with seven pounds off his back is a good thing for Taj Dragon," Ng said. "We want to get him ready for the Group 3 race (Lion Rock Trophy Handicap) on 2 June and to keep him race fit so we don't have to go any trials.
"He's been doing very well since he won the Group 3 (Chinese Club Challenge Cup Handicap on 1 January), running in the Group 1 and Group 2 races and his last run he didn't have the best chance to finish off with the track conditions, but he still got sixth. I think he has a good chance on Sunday."
Lui will be represented by Packing Treadmill and Wonder Kit in Sunday's feature along with first starters Harold Win and Winning Day, High Rise Power, Silver Sonic and the consistent Patch Of Theta on the undercard.
In the midst of another strong season, David Hall hopes Atullibigeal can prevail under Zac Purton from the outside barrier of gate six in the Racing Heritage Handicap.
"He's a consistent horse, runs well all the time. Handicap race for him is probably a good opportunity. He perhaps might be looking for a little bit longer these days, but hopefully he's still got a bit of freshness in his legs at 1400 (metres)," Hall said.
Hall is also optimistic Champion Instinct can return to winning form in the Class 3 Levade Handicap (1200m) after Hasten Delight brought the gelding's three-race winning streak to an end on 7 April.
"He (Champion Instinct) had a tough run. He had a bit of an ordinary draw and was working on a fast speed to get to the position he had to. He was a little bit weak late (finishing fifth) but he's still in good order," Hall said.
"He's a healthy horse and hopefully he can have a bit more of an economical run and we'll see how he measures up at the grade."
Sha Tin's 10-race card starts on Sunday (19 May) with the Class 5 Ownership Pride Handicap (1200m) at 12.45pm.
