Less than a week after crafting the fight plan that paced his fighter to a glorious upset accompanied by an onslaught of brutal left hooks, trainer Derrick James has delivered a mighty legal punch of his own to former welterweight champion Errol Spence Jr.

James has filed a lawsuit in Dallas County, Texas, seeking “no less than $5 million” from Spence for fraud and breach of contract for failing to fulfill promises to pay the trainer a 10 percent cut of his purse money – for bouts including Spence’s one-sided ninth-round TKO loss to Terence Crawford in July.

The lawsuit claims James “discovered Spence’s breach of contract, fraudulent business practices and misrepresentations after Spence received the $25 million guaranteed fight purse” for Crawford, but only first paid James $350,000 after his first, crushing defeat.

Spence has not commented on the matter.

Spence is reportedly bound to work with a new trainer while James directed Ryan Garcia to an upset of 140-pound champion Devin Haney on Saturday in New York, and is now preparing Frank Martin for a June 15 title shot against unbeaten Gervonta Davis.

In a Feb. 13 conversation, the lawsuit claims, Spence told James he “was not entitled to receive 10 percent of his guaranteed purse. … Spence asserted someone named ‘Al’ told him that paying James $350,000 for the Crawford fight in exchange for his training services was ‘generous.’”

Whether that individual is Spence’s longtime manager and Premier Boxing Champions head Al Haymon was not confirmed in the lawsuit.

James’ attorney wrote in the lawsuit that “no one named ‘Al’ was present when James and Spence originally entered into their agreement. … Any alleged reliance by Spence on advice from someone named ‘Al’ regarding James’ compensation is misplaced.”

Spence, the lawsuit claims, wound up telling James in a Feb. 15 phone call that he “did rob” James by shorting him, and added in a text message the next day that he “wanted to own up to his own s**t” and pay James the remaining $2.15 million that kept with their verbal agreement.

The fighter, according to the lawsuit, said the money would arrive the following week because he lacked “liquid” funds, but the remaining cut never arrived.

James’ attorney, Adraon D. Greene, wrote in the lawsuit that, “Unfortunately, ‘The Truth’ [Spence’s nickname] once again proved that he could not be trusted because he reneged on this written agreement to pay.”

James and Spence had worked together since before the 2012 Summer Olympics in London.

Their disagreement hinges on what constitutes a guaranteed fight purse. Spence is promised funds from a bout agreement, but he also receives the upside of pay-per-view sales, which send his total earnings spiraling upward.

Spence has not provided accounting for his pay-per-view bouts including victories over Mikey Garcia, Shawn Porter, Danny Garcia, Yordenis Ugas and Crawford.

Yet Spence’s text message to James asking, “What’s the number [owed]? $2.15 million? Since I already paid you $350,000?” indicates acknowledgement of the 10 percent arrangement they kept throughout the years, James attorney claims.

“Mr. James relied on Mr. Spence’s promise to pay the full amount for the labor and services rendered,” attorney Greene wrote in the lawsuit. “Mr. Spence has failed to pay the full amount to Mr. James.

“The conduct of Mr. Spence is intentional, willful, malicious.”