As a 2-yard Melvin Gordon run pushed San Diego to Kansas City’s 42-yard line early in the fourth quarter on Sunday, the Chargers had a 99.9-percent chance for victory, according to Pro-Football-Reference’s win probability model. Down 27–10, the chances for a Chiefs comeback were beyond bleak.

Three plays later, Chargers kicker Josh Lambo missed a 54-yard field goal, and the Chiefs put together a furious comeback over the final 11 minutes and 20 seconds. They tied the game in regulation, then won it in overtime.

The transition is still ongoing, but one thing is clear: These aren’t last year’s Chiefs.

Due to Andy Reid’s reputation for clock mismanagement, a deliberate ball-control and run-heavy offense, and a quarterback nicknamed “Captain Checkdown,” “explosive” has never been a word anyone’s used to describe the Chiefs. But when we saw them last, it was almost like they were in on the joke.

Down 27–13 with 6:29 left in the divisional round of the playoffs against New England, Kansas City trundled downfield, putting together a 16-play, 80-yard drive that culminated in a 1-yard touchdown run by Charcandrick West. That score cut the Patriots’ lead to seven, but the 5:16 of drive time left the Chiefs with just over a minute to get the ball back and score. New England recovered the onside kick attempt, grabbed a quick first down, then kneeled the game out for the win.

In fact, the Chiefs showed a near-historic lack of urgency. It was the second-slowest “we’re down two scores with under seven minutes remaining” drive in over 2,200 such instances across the league since 1998. By taking so long, the Chiefs virtually eliminated any chance they had to win the game.

The divisional-round slowdown drive wasn’t necessarily anything new for last year’s Chiefs, either. It never really mattered much what the situation was; they ranked near the bottom of the league in almost every tempo category: 31st in total seconds per snap, 29th in seconds per snap in the first half, 32nd in seconds per snap in the second half, 28th with a big lead, and 25th while trailing by more than seven.

Over the offseason, Reid decided that the pace needed to be picked up. From Week 7 of last year, Doug Pederson called the Chiefs’ plays in the second halves of games, but he’s now the head coach in Philadelphia, so the play-calling onus has fallen back onto Reid’s shoulders. Reid, along with his two new offensive co-coordinators, Brad Childress and Matt Nagy, removed some plays from the two-minute drill to simplify the call sheet, and he cut down the verbiage of the tongue-twisting, West Coast–offense play calls that sound like jibberish to the untrained ear, like “shift to halfback twin right open, swap 72 all-go special halfback shallow cross wide open.” Quarterbacks often bring two or three play calls into the huddle to use as audible/check options, so in a hurry-up situation, simplicity is key to avoid making the signal-caller recite multiple long-winded calls as the clock ticks away.

As soon as the Chiefs got the ball back after Lambo’s missed field goal on Sunday, Reid put his team into this newly calibrated hurry-up mode. And unlike against New England, they ran the offense primarily from the no-huddle, where hand signals and code words replaced play calls, and the tempo ensured they’d get enough possessions to cut down the 17-point deficit.

The next three drives did exactly that: The first took just over two minutes off the clock and ended with a Jeremy Maclin touchdown; the second took three minutes and 40 seconds and netted them a field goal; and on the third and crucial drive that started just after the two-minute warning, the Chiefs took just 46 seconds to gain 42 yards and punch the ball in to tie the game. Reid’s play-calling was masterful and showed an understanding of how to keep Alex Smith in a rhythm: He exploited soft coverage with dump-offs over the middle to his tight ends and running backs and quick throws to his receivers on the wing, and when he identified the biggest weakness in San Diego’s defense — Manti Te’o’s lack of range in coverage — he repeatedly attacked it by sending running backs Spencer Ware and Charcandrick West out of the backfield on routes to the outside. He even threw in a couple of strategically placed draw plays to keep the Chargers honest up front. That was standard Kansas City fare, but done at lightning speed.

Of course, an effective game plan doesn’t matter without a quarterback to implement it, and Smith made several big-time throws down the field; he looked nothing like “Captain Checkdown.” The ball location on the first touchdown throw was absolutely perfect, and Jeremy Maclin didn’t have to lift his hands — the “ball is coming” tell that cornerbacks look for in coverage — until the last second.

Later in the fourth quarter, he hit Maclin over the middle, threading the needle among three Chargers defenders to move the ball inside the 10-yard line. It looked like Smith initially wanted Maclin on the slant, but when cornerback Brandon Flowers dropped into that passing lane, he had to adjust. He reset his feet and threw to the hole between the San Diego defenders.

This wasn’t the Chiefs offense that we’re used to seeing. They’ve been efficient the past two years, ranking sixth in offensive DVOA in 2015 and 12th in 2014. Much of their potency comes from their elite run game (which finished first in rush DVOA in 2015 and fifth in 2014), but they haven’t been as effective in the passing game, ranking 14th in passing DVOA both years. A big reason for that has been Smith’s reticence to push the ball down the field; they finished 28th in the NFL in passes of 20 or more yards last year, and 29th in 2014. That changed on Sunday, as they finished the game with five passes of 20-plus yards, tied for fifth most in Week 1.

Now, with the score back even, the offense could’ve reverted to its conservative roots in overtime, but Smith kept his foot on the pedal. The first play of their game-winning drive went for 20 yards, as Smith evaded pressure, kept his eyes downfield, and lofted a perfect pass to Ware up the sideline.

Several plays later, Smith made another pretty back-shoulder throw, this time to tight end Travis Kelce.

To cap things off, Smith audibled into an option run play — and the quarterback kept it himself for the game-winning touchdown.

After a quiet first half in which he completed nine of 15 passes for 94 yards, Smith exploding during the higher tempo of the second half and overtime. He finished the game 34-of-48 for 363 yards, with two touchdowns and one interception, in addition to 15 yards rushing and that clinching touchdown. He’s never attempted or completed more passes in a single game, and the 363 passing yards was the second-highest total of his career.

In almost all of his first eight seasons in the league, Smith had to learn a new offense. Now, at age 32, it seems he’s finally found stability with Reid in Kansas City, as this is his fourth season in the same system. On Sunday, he showed more comfort and confidence within the offense than we’d ever seen before.

Most of the main offensive pieces remain from last year, but they carry the potential of a higher-octane offense than we’ve seen. Maclin arrived last year as the team’s true no. 1, and that hasn’t changed (he had five catches for 63 yards and a touchdown on Sunday), while 2015 third-round pick Chris Conley is emerging as the team’s second wideout (four catches for 43 yards). At tight end, Kelce (six catches, 74 yards) has earned the nickname “Baby Gronk” for a reason: He’s big and fast, and can block, catch, and score touchdowns. And even without Jamaal Charles, who continues to recover from a torn ACL, the running backs group is as solid as any in the NFL: Ware was incredible on Sunday (11 carries, 70 yards, and a TD to go with seven receptions for 129 yards and another score) and West did his part in the passing game (six catches, 24 yards).

Now, the Chiefs probably haven’t suddenly transformed into a top-10 passing offense, but the changes that Reid implemented over the offseason seem to have made them capable of putting points on the board quickly. And while Smith was predictably efficient with his underneath throws, when he was asked to attack the defense, he delivered the ball on time, with accuracy, down the field. This is the dimension the Chiefs offense has been missing the past few seasons, and if Smith can continue to aggressively challenge corners and safeties downfield, it’ll make Kansas City so much more difficult to defend. No more stacking the box to stop the run. No more cheating toward the line of scrimmage. A team that can slowly grind you to dust with its run game when it has a lead, but then hit the turbo when it really needs to score points quickly — that’s a dangerous thing. Add in a great defense — which limited the Chargers to two field goals in the second half — and Kansas City looks like a legitimate threat in 2016.