SAN DIEGO – The first time Philip Rivers saw Patrick Mahomes fling passes as an opponent, Rivers talked like he'd just seen the NFL's next great quarterback.

"He has a chance to be really, really, really, really good," Rivers said after Mahomes led the Chiefs past the Chargers in the 2018 season opener.

Rivers being no dummy about football, it was an ominous comment, in retrospect, for the Chargers quarterback and his team.

Mahomes, a Texas Tech alum who reminded Chiefs coach Andy Reid of Brett Favre as a young gunslinger, was quick to become what Rivers said he someday could be.

The irony is Rivers took the biggest initial hit from Mahomes taking over the Chiefs, because the AFC West title remained out of reach despite Mahomes' inexperience. Having outlasted Peyton Manning, who'd led the Broncos to four West titles and two Super Bowls after joining the division, Rivers didn't outlast Mahomes. Soon after Mahomes won Super Bowl MVP honors this month, the Chargers moved on from Rivers, 38.

Now comes word of a thought-provoking subplot, involving Rivers and Mahomes, from the 2017 draft.

The Chiefs, in their quest to trade up and draft Mahomes, had terrifying visions of someone else drafting him first.

That team's colors were blue and gold.

The Chiefs feared the Chargers had the same plan of drafting Mahomes and stashing him behind a veteran quarterback. Even scarier to Chiefs leaders, the price to the Bolts would pale in comparison; while the Chiefs had decided to deal three premium picks to climb 17 spots and draft Mahomes at No. 10, a 5-11 season had given the Chargers the No. 7 pick overall. They could just grab him.

For several weeks, the prospect of this thunder bolt of lightning kept Chiefs bosses on edge.

"At the end of the day the only one I was scared of was San Diego," John Dorsey, the Chiefs' general manager then, told The Athletic's Bob McGinn before the Super Bowl. "They were at 7. That's the one I worried about more than anything in the world. Philip Rivers was 35 (the previous season). Once they took Mike Williams, we said, 'We got this guy.' "

What Dorsey meant is that when Chargers bosses paired Williams, a 6-foot-4 ball-hawking receiver from Clemson, with Rivers, the Chiefs knew no other team would select Mahomes before they could trade with the Buffalo Bills to get the 10th pick.

For Chargers leaders huddled in Mission Valley that April, not taking Mahomes was the franchise's final big football decision of the San Diego era before the franchise moved north.

Was this San Diego karma at work, biting Team Spanos for the rude way it handled the relocation?

Soon after Mahomes joined the Chiefs, a back injury felled Williams in his first team practice in San Diego, leading to a disappointing rookie year.

Dorsey's comment about fearing the Bolts may seem a stretch, given their devotion to Rivers.

Since 2007, the first draft after Rivers logged his first season as a starter, the Chargers were the only NFL team not to draft a quarterback in the top four rounds.

Yet going into the Mahomes draft, the Chargers' and Chiefs' quarterback situations were parallel in two main respects: Rivers was deep into his career and had three years left on his contract, while the Chiefs' Alex Smith was only two-plus years his junior and had two years left on his deal.

So, whether the Chiefs or Chargers drafted him, Mahomes would sit as a rookie while a veteran starter led a Super Bowl bid.

Of the two vets, the better career had belonged to Rivers, an eight-time Pro Bowler.

But Smith, obtained in a March 2013 trade with the 49ers, had made big strides under Reid.

While their styles make comparisons dicey – Smith, a hybrid playmaker; Rivers, strictly a pocket passer – Smith's progress pulled him to near Rivers in overall effectiveness. The Chiefs had gone 41-20 under Smith, while the Chargers were 27-37 under Rivers.

In fairness to Rivers, while Smith could lean on Reid – a Hall of Fame-level coach who commanded a top-tier salary and had the chops to assert himself in personnel moves if he wanted to – the same four years marked the Mike McCoy era in San Diego. McCoy hasn't returned to head coaching since Dean Spanos hired him to run the 2013 Chargers. After the team let him go in January 2017, McCoy was fired each of the next two seasons as coordinator of a QB-deficient offense.

Reid increasingly made effective use of Smith's agility and foot speed, adding explosiveness to the offense. Protecting the ball while also mastering option plays and movement throws, Smith made a habit of matching or outplaying Rivers.

In the final two seasons before each West rival made its Mahomes decision, Smith outpointed Rivers in quarterback rating, which takes into account rushing. Rivers had the better passer rating, 95.1 to 92.2, in their four years up to 2017.

But with Smith unable to get the Chiefs past the divisional playoffs, the brain trust of Reid, Dorsey and Dorsey's successor, Brett Veach (a big fan of Mahomes) moved on from their veteran quarterback.

This took guts. But it was a brilliant move.

Don't forget that Smith did his part, too. He shared hard-earned NFL wisdom that Mahomes deemed invaluable. Also, he created good trade value by having a career-best 2017 season.

Did Chargers bosses, led by GM Tom Telesco and John Spanos, whiff by not drafting Mahomes?

That's an easy conclusion to make, in hindsight. But the bet on Williams wasn't a bad one, and Rivers, showing that doubling down on him wasn't dumb, had one of his best seasons in 2018 to lead the Chargers to their top record in six years, a 12-4 mark. Rivers remained durable, missing no starts or meaningful snaps in the three years after Mahomes was drafted.

Take nothing from Mahomes, whose tremendous passing ability enhanced the whole team, but few quarterbacks have been drafted into such a fertile environment. The Chiefs paired him with a great head coach, a lot of playmaking talent headed by All-Pros in Travis Kelce and Tyreek Hill and a very good right tackle in Mitchell Schwartz plus solid left tackle Eric Fisher. Smith was an ideal mentor who bought him a developmental year.

Bolts fans may disagree, but it's better for football lovers that Mahomes joined the Chiefs instead of Team Spanos.

The pairing has produced the NFL's most exciting offense the past two years.