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One of the more controversial decisions the San Francisco 49ers made this offseason was letting Donte Whitner leave in free agency, and signing Antoine Bethea to take his place.

The difference between Whitner’s four-year, $28 million contract and Bethea’s four-year, $21 million contract (both via Spotrac) seemed small enough that the apparent downgrade from Whitner to Bethea was questionable, at best.

Four games into the season, however, and the deal looks like a great one for the 49ers. Bethea is currently ranked as the top safety in football, according to Pro Football Focus’ charting stats (subscription required), while Whitner is hanging down in 57th place. Bethea’s been a force both in pass coverage and run defense, providing a veteran presence to a very young secondary.

Bethea’s not only tied with Patrick Willis for the team lead in tackles, but he also leads the team in stops, via PFF. Ten of his 22 solo tackles have caused the opposing offense to fail on a down—it’s one thing to make a tackle downfield after a 30-yard gain, and another thing entirely to come up from the safety position and make a tackle that stops a team dead in its tracks.

Bethea’s high level of play continued against Philadelphia, adding four stops to his season total and providing consistent tight coverage in the passing game. While Bethea was quick to dismiss his play as being part of “a team effort” after the game, he drew the praise and admiration of his coach and teammates.

"Words can’t describe some of the plays he made out there today," linebacker Patrick Willis said after the game. "He was all over the place. There is no question that if I could give a defensive game ball, it would absolutely go to our secondary, him in particular."

“He was huge”, coach Jim Harbaugh added. “Had some PBU's, had the interception, sharp, crisp tackling, again.”

While Bethea provided a high level of play throughout the game, including a key tackle on the goal line stand to preserve the lead late in the fourth quarter, you don’t have to watch the entire game to see what impact Bethea can have on a team. Just sticking to the third quarter of the game, you can see Bethea’s work in both pass coverage and run defense, and how they impacted a game. On three consecutive drives, Bethea made great plays as the 49ers made their comeback.

The Forced Fumble

With the Eagles leading 21-13, they began a drive in an attempt to get something going on offense and increase their time of possession. Nick Foles found his tight end Zach Ertz, lined up as a slot receiver, uncovered on a little quick out. Bethea, a good ten yards down the field, sprints up to make the tackle.

NFL Game Rewind

He doesn’t just make the tackle, however. Bethea pries the ball loose with his left hand. It pops straight up, and Perrish Cox plucks it out of the air for a key turnover.

NFL Game Rewind

"Forced fumble, just running to the ball, trying to make a tackle and I was able to get my hand in. It's something that we focus on throughout the week, forcing turnovers,” Bethea said after the game, and it couldn’t have come at a better time for the 49ers. A long drive by Philadelphia there could have sent the game spiraling out of reach, but the turnover flipped the momentum and brought the 49ers back into the game.

Stout Run Defense

Bethea made plays in the run game all day long. As a unit, the 49ers allowed only 22 yards rushing, the ninth-lowest total they’ve achieved in the NFL. Bethea was responsible for six tackles in the run game, including a key force out the drive after the forced fumble.

On 1st-and-10, the Eagles tried a run around the right, but their offensive line caved in, closing up all the rushing lanes. There are very few running backs in the league better than LeSean McCoy at reversing field and making big plays, and that’s precisely what he tries to do here.

NFL Game Rewind

Bethea, however, stays home on the backside. While it would have been very easy for him to overpursue and back up the play on the right, he remains at home. You can see in this screenshot that Bethea is literally the only defender remaining on the left side of the field when McCoy cuts back; if he gets around Dan Skuta, there’s literally no one else stopping him from racing 80 yards to the end zone.

NFL Game Rewind

Bethea comes up and forces McCoy out of bounds at the line of scrimmage. The next running play gets stopped after five yards, and the ensuing pass is incomplete, forcing a three-and-out. It all starts from that great play on first down, which helped force the Eagles into a more predictable offense. Bethea didn’t make any amazing highlight plays against the run, but he was solid throughout the entire game.

The Interception

On the drive after that, with the 49ers having taken a 23-21 lead, Bethea added another dagger to Philadelphia’s heart. Nick Foles, pressured and hurried by Justin Smith, gambled with a long pass down the center of the field towards Jeremy Maclin.

“The pick,” Bethea said after the game, “[I] was able to go up there and Justin Smith was able to get some pressure on the quarterback and I was able to go up and make a play."

That’s precisely what happens—Bethea, playing as a single deep safety, undercuts Maclin, avoids colliding with Perrish Cox, and comes down with an interception.

NFL Game Rewind

It was a momentum-altering play. Against the Chicago Bears, there was a similar situation, with Cox and Bethea covering a deep route down the middle of the field. The ball was underthrown again, and Bethea went up for the interception. But that time he and Cox collided and the ball fell harmlessly to the turf. The Bears went on to score a touchdown, and the comeback was on.

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The more successful outcome against Philadelphia shows that Bethea’s getting more comfortable working with the secondary—this time, the two defenders are able to adjust to avoid colliding. We saw against the Bears how quickly a game can turn around, and the 49ers simply would not let the Eagles dodge this bullet.

Three consecutive drives in the third quarter, Bethea made a huge impact on the game. Over the course of that period, the 49ers went from down eight points to up two, and they wouldn’t trail again the rest of the way. Bethea continued that high level of play throughout the game, but these three drives were emblematic of the impact he had.

Donte Whitner was a great player, but Bethea’s been so good in his place that former strong safety hasn’t been missed. Count this acquisition as a great offseason move by the front office.

Bryan Knowles is a featured columnist for Bleacher Report, covering the San Francisco 49ers. Follow him @BryKno on twitter.