Justin Upton, left, is restrained by teammate Matt Williams after being hit with a pitch against the Washington Nationals during a game on June 5, 2011, in Phoenix. (AP Photo/Arizona Republic, David Kadlubowski)

With a stunning, but not entirely unexpected, move Thursday morning, the Nationals’ long trek to defending their National League East crown, and potentially more, got tougher. The Atlanta Braves, their fiercest division foe, agreed to ship their versatile fielder and hitter Martin Prado, in his last year before free agency, along with four prospects to the Arizona Diamondbacks for two-time all-star slugging outfielder Justin Upton and third baseman Chris Johnson, according to several reports.

The addition of Upton reunites him with his brother B.J. Upton, 28, who the Braves signed to their most lucrative free agent deal ever, a five-year, $75 million contract this winter. With the Upton brothers and Jason Heyward, the Braves should be among the elite outfields in baseball — rivaling the Los Angeles Angels of Anaheim (Mike Trout, Josh Hamilton and Peter Bourjos) and the Nationals (Denard Span, Bryce Harper and Jayson Werth).

The Braves once-left-handed heavy lineup is now balanced with two power-hitting right-handers (the Uptons), the reunion of the brothers should help them perform (Justin Upton, 25, now likely calmed from the years of trades rumors surrounding him in Arizona) and they shipped away Prado (whom they reportedly struggled to sign to a long-term extension). The Braves have watched the Nationals bolster their team this offseason and, a month away from players reporting to spring training, they made their rebuttal.

But for those proclaiming the Braves as perhaps the best team in the National League, there’s enough to give pause. The Braves will indeed have a dangerous and elite bullpen (with Craig Kimbrel, Jonny Venters and Eric O’Flaherty) and a stacked and balanced lineup — but the starting rotation isn’t on par with the Nationals or Cincinnati Reds or San Francisco Giants.

Last season, the Braves rotation endured a rash of injuries. But next year’s likely rotation of Mike Minor, Tim Hudson, Paul Maholm and Kris Medlen (and Brandon Beachy returning from Tommy John surgery) isn’t  as imposing, nor proven, as Stephen Strasburg-Gio Gonzalez-Jordan Zimmermann-Ross Detwiler-Dan Haren. Nor is it better than the Reds’ Johnny Cueto-Mat Latos-Homer Bailey-Bronson Arroyo-Mike Leake/Aroldis Chapman or Giants’ Matt Cain-Madison Bumgarner-Ryan Vogelsong-Tim Lincecum-Barry Zito.

Overall, an outfield of Upton-Upton-Heyward is exceptional but both Upton brothers, though young and gifted athletes, aren’t the same as Prado-Michael Bourn-Heyward. By the standards of some advanced defensive metrics, Prado and Bourn were better outfield defenders than the Upton brothers. According to the UZR/150 metric on Fangraphs.com, Harper and Span rank in the top 10 over the past three seasons (though Harper only played last year) and Justin Upton is 18th and B.J. ranks 27th.

Of course, the Braves are essentially trading away one more year of Prado and letting Bourn walk in free agency for three years of control of Upton-Upton-Heyward. And, they are trading away the on-base percentage, batting average and stolen bases of Prado-Bourn for the slugging and power of the Uptons. And Heyward, only 23, could cancel it all out, as he has the potential to be among the best ten players in the game next season with his power, fielding and speed.

The Braves will also have two potential weaknesses to contend with. Chipper Jones now retired, they will likely platoon third base between Johnson and Juan Francisco. Adrelton Simmons, their prized, slick-fielding shortstop, figures to be their everyday leadoff hitter, a role he has yet to fill.

As a team, the Nationals likely still hold the edge over the Braves in overall team fielding; their infield among baseball’s elite and their outfield as good as any. Offensively, the Braves will have plenty of power but also a ton of strikeouts. B.J. Upton struck out 169 times in 2012 and Justin Upton fanned 121 times last season, and now join Heyward (152 times), Dan Uggla (168) and Freddie Freeman (129). Span, the Nationals’ lineup addition, struck out  only 62 times last season, and an improved Harper and potentially Danny Espinosa could help bring down last year’s high-strikeout total.

The 19 meetings — or potentially more — between the Nationals and Braves next season have the potential to be more exciting and well-played than last year’s heated contests. It took the Nationals until the final week of the season to clinch last year’s division crown because of the surging Braves. Both teams have made moves this winter to bolster their chances of winning, the Braves’ recent trade for Upton the latest indication they will not allow the Nationals to claim the division so easily.

Here are the potential lineups of both teams side-by side:

Atlanta — Washington

Andrelton Simmons (R), SS — Denard Span (L), CF

Jason Heyward (L), RF — Jayson Werth (R), LF

Justin Upton (R), LF — Bryce Harper (L), RF

Brian McCann (L), C — Ryan Zimmerman, 3B

B.J. Upton (R), CF — Adam LaRoche (L), 1B

Freddie Freeman (L), 1B — Ian Desmond (R), SS

Dan Uggla (R), 2B — Danny Espinosa (S), 2B

Juan Francisco (L)/Chris Johnson (R), 3B — Kurt Suzuki (R)/Wilson Ramos (R), C

Who would you take? Position-by-position?