Mac Robertson has long been king of the hill during summers at Canterbury Park in Minnesota, winning six consecutive trainer titles between 2005 and 2010. When he brought a string of horses to Delaware Park for the first time last season, however, Robertson didn’t make much of an impact.Robertson finished in a tie for 24th place at Delaware, winning with 12 of 88 starters, 45 percent of whom finished in the money. Those are respectable figures, but nowhere near the flashy stats he posted with his Canterbury string. Those runners went 51 for 148 (34 percent) with a phenomenal 66 percent in the money.Flash forward to this spring and Robertson’s fortunes at Delaware have improved. He came into last weekend with 7 wins in 22 starts (32 percent), tied for fourth in the standings, with 64 percent of his horses finishing in the money.Robertson will look to improve upon those numbers when he sends out the 3-year-old colt Forgotten Knot in Monday’s featured ninth race, a first-level optional $50,000 claimer at a mile and 70 yards on the main track.Forgotten Knot comes back just 12 days after rallying from eighth to get third in his turf debut. In his last appearance on dirt, Forgotten Knot finished second in a first-level allowance at Oaklawn Park. The 84 Beyer Speed Figure he earned for that race two months ago is the best number among the eight 3-year-olds in Monday’s field.The two prime threats to Forgotten Knot are Dinny Dinosaur, whose 3 wins in 13 starts make him the most successful horse in Monday’s field, and Major Prince, who has been off since romping by 7 1/2 lengths against maiden special weight company at Oaklawn in late March.Dinny Dinosaur set the pace and led until deep stretch while running against older horses on opening day at Delaware. He raced against the grain of a track that favored come-from-behind horses in routes and earned a career-best 82 Beyer. The horse who finished ahead of him, Tech Fall, came back to record a 91 Beyer next time out.Major Prince comes from the high-percentage barn of Larry Jones. After four losses to begin his career, Major Prince jumped up to an 80 Beyer last time out. Jones is just 1 for 4 with last-out maiden winners returning in a dirt route after 61 to 180 days on the sidelines.