Four weeks into the season, the debate over the NFL's best team has a clear answer, at least according to ESPN.

The San Francisco 49ers climbed from second to first in the network's Week 5 Power Rankings, and nothing about their 4-0 start suggests they're keeping the seat warm for someone else.

San Francisco took care of Denver 24-14 at Levi's Stadium on the same weekend Buffalo stumbled against New England, and the door swung open.

Kansas City and Minnesota are the only other teams still without a loss, but neither has stacked up quality wins the way the Niners have.

The 49ers have put up 122 points while giving up only 64, for a +58-point differential that leads the league.

The offense ranks near the top in scoring, the defense ranks near the top in keeping teams off the board, and that two-way consistency is hard to find this early in the year. 

Victories over the Rams and Broncos mean the 49ers have already passed two real tests, and the offensive line deserves its share of credit.

Through four games, Purdy hasn't been sacked once, even against two fronts built to get after the quarterback.

What should worry the rest of the league most is how San Francisco beat Denver.

The offense struggled to find a rhythm early, and the game sat tied at 3-3 before a Broncos mistake gave the Niners an opening.

Instead of pressing, they trusted the defense and special teams to hold the line until Purdy, Christian McCaffrey, Deebo Samuel, and George Kittle finally broke things open in the second half.

Purdy has rightfully drawn early MVP buzz, and the offense has carried the load for most of the first month, but a contender needs a plan for the days when the points don't come easily, and Sunday proved the 49ers have one.

They've done it shorthanded, too, which has become a habit in Santa Clara. Trent Williams and Mike Evans were both banged up the week prior and still suited up against Denver. Depth and durability aren't flashy, but they're a big reason this group keeps stacking wins.

Now the real work begins. Earning the top spot is one thing, but defending it on the road is another.

Week 5 sends San Francisco to Seattle to face the Seahawks, ranked third by ESPN, and Vegas has the Niners as three-point underdogs.

A division rival, a loud stadium, and a defense that can make life miserable: it's the right kind of test for a team wearing the crown.

Win, and the 49ers move to 5-0 with a two-game edge over Seattle in the NFC West. Lose, and the division tightens while Kansas City makes its case for No. 1.

Either way, San Francisco has earned the benefit of the doubt. The best point differential in football, an unbeaten record, and wins over legitimate competition add up to the league's most complete team through one month.