COSTA MESA – Last February, shortly after he was hired as the Chargers new receivers coach, Phil McGeoghan sat down to study tape of Mike Williams.

There wasn’t much to watch. Williams’ rookie season had been plagued by injuries. Painful stiffness in his back lingered from his first NFL practice on, robbing him of OTA’s, training camp and more than a month of the season. When he did return, Williams’ integration on offense was painfully slow for the highest-drafted receiver in franchise history. “It was just hard for him to get back into a groove,” quarterback Philip Rivers explained.

As the Chargers missed the playoffs, Williams finished with just 11 catches for 95 yards. His catch rate (47.5 percent) ranked third-worst among all qualifying rookie wideouts.

McGeoghan first met Williams a year earlier at the NFL Scouting Combine. He’d seen enough of his Clemson tape to have some idea of the potential the 6-foot-4 wideout possessed. What McGeoghan wondered most about was everything else. How did he do with the little things? How did he run routes? How did he run block? Was he consistent?

McGeoghan didn’t like what he saw. “My immediate thought was, ‘Wow, we have a lot of work to do,’ ” he said.

Ten months later, that tireless work is paying tremendous dividends as the Chargers thunder towards the playoffs, with a serious shot at the top seed in the AFC. They couldn’t have gotten this far without Williams, who’s become one of the league’s premier red-zone threats in his just second season, tallying 10 total touchdowns through 15 weeks.

Last Thursday, he scored three times in a breakout performance in Kansas City, the last of which came with only four seconds remaining. One play later, he ran wide open for the game-winning two-point conversion. The game earned Williams AFC Offensive Player of the Week honors and seemed to signal his arrival, but beyond that, for Williams and his wide receivers coach, it was proof of how much a new mindset could make the difference.

The two men were not exactly a natural fit. “It wasn’t great at first,” McGeoghan admits now. “He was a little too chill for me.”

Williams, meanwhile, had never had a coach with McGeoghan’s intensity. During offseason film study, they butted heads, as McGeoghan laid out the many missteps he’d seen Williams make as a rookie. McGeoghan didn’t like Williams’ “aura” around the facility, and he told him as much. He thought he looked complacent, like he’d already arrived. He wondered if Williams understood just how urgent it was that he live up to expectations.

“I couldn’t tell by his body language,” McGeoghan said. “At first, I looked at this chill attitude like, man, maybe this isn’t that important to him.”

That suggestion grated at Williams. To him, nothing could be further from the truth. He wanted so badly to be great. He wanted to live up to the hype of his draft position. He wanted to put the lingering injuries and disappointment from his rookie season behind him.

“Nobody wants to be stuck in those ways,” Williams said. “I wanted to find ways to get better in my game.”

At the start of training camp, McGeoghan watched Williams closely from the sideline during a run-heavy period of practice. The young wideout wasn’t getting the ball, and he wasn’t happy about it. He started sloughing off blocks. A frustrated McGeoghan let his wideout hear about it, he says, “at an elevated volume.” For the rest of practice, Williams blocked with a fervor none of the coaches had seen before. “Like a madman,” McGeoghan says.

That night, Williams and McGeoghan sat down in a meeting room at the team hotel and hashed things out. Williams told him he desperately wanted to be great. It was all McGeoghan needed to hear.

“This is professional football,” McGeoghan said. “He’s a grown up who pays his taxes, so I talked to him like a man. If you want to live up to where you’re drafted, if you want to have a better season, this is what you have to do.”

He needed to focus on the details. Running crisper routes, and running them at the right depth. Blocking with more technique. Taking care of his body. Focus on those little things, he told him, and the big moments would take care of themselves.

The next day, Williams went over the top of a Chargers defensive back to pull down a stunning, high-point catch. The transformation seemed almost instantaneous. “To be honest with you,” McGeoghan says, “he hasn’t stopped making plays like that since.”

In the weeks that followed, coach and player grew closer. After each camp practice, the two spoke in his office for 15 minutes or so, sharing stories from their childhoods, talking about anything but football. Before long, McGeoghan began to better understand how the young wideout ticked. The trust between them continued to build. Then, things started to click for Williams.

“I started doing the little things,” Williams says, “and after that, I started to get the ball more.”

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Patrick Mahomes’ late scrambles too much for Joey Bosa, Chargers He’s been on an steep, upward trajectory ever since, catching 39 passes for 592 yards this season. In the Chargers’ spread-the-wealth offense, Williams is not yet a focal point; though, with Keenan Allen a game-time decision against the Ravens, he could be on Saturday. Either way, in the midst of a mindset-changing second season, Williams has taken a huge leap forward.

“He hasn’t had the 60, 70 catches this season,” Rivers said, “but he’s had a ton of big ones. It’s been great to see him come on.”

McGeoghan agrees. “This guy has an unbelievable ceiling,” he says. “He just has to keep refining the little things.”

And when he does, even bigger performances are sure to come.