Redskins linebacker Ryan Kerrigan (91) goes for the ball held by Buffalo quarterback Tyrod Taylor. (John McDonnell/The Washington Post)

The Washington Redskins emerged from their 21-16 preseason win over the Buffalo Bills having gained some much-needed clarity at two key areas of their defense — inside linebacker and defensive line.

Joe Barry and his defense entered training camp with most of the starting jobs nailed down. But uncertainty loomed over the second starting inside linebacker position, and Barry also needed defensive linemen to distinguish themselves as he tried to settle on a rotation that would be improved both against the run and the pass.

Friday night, Mason Foster seemed to put his stamp on the inside linebacker spot next to last year’s leading tackler, Will Compton. Rookie Su’a Cravens took another step forward in his quest for a key role at that same position, which Barry calls “the Moe.” And defensive lineman Ziggy Hood put on an impressive performance while getting the start at right defensive end, continuing an already-strong preseason showing.

Foster entered the game with an apparent leg up on challenger Perry Riley Jr. But he felt like he needed another strong performance to cement his status after splitting time with Riley since the start of training camp.

Entering their sixth and seventh NFL seasons, respectively, both Foster and Riley have proven themselves capable.

Foster signed with Washington midway through last season, recorded 37 tackles in five starts and helped improve Washington’s run defense late in the season. Riley, meanwhile, had started for the better part of the past five seasons for Washington before breaking a bone in his foot and making way for Foster. While Foster excelled against the run, Riley seemed more effective in pass coverage.

Meanwhile, because of his versatility and abundant potential, Cravens has seemed on the verge of forcing his way into the discussion after being restricted to the second unit for the first half of the preseason.

Foster turned in an authoritative performance against Buffalo, racking up four first-quarter tackles to lead a first-team defense that held the Bills’ starting offense to 38 rushing yards.

All the while, Barry’s vision for Cravens became more distinct. Cravens took over for Foster on third downs when Washington used its dime packages, which called for the Southern California product to drop back into coverage or, at times, rush the passer. Cravens broke up a pass on the first defensive stand of the game, and appeared to play well in his coverage assignments.

The Foster-Cravens rotation seemed to work seamlessly as Washington’s defense denied the Bills on all six of their first-half third down conversion attempts.

However, because of their effectiveness, the two could have bumped Riley — who didn’t record a tackle — out of the equation. With the 2010 fourth-round pick set to earn $5 million this year, the Redskins could opt to go with a younger, more affordable backup, such as Terence Garvin, who has played well on defense and special teams since signing with Washington this offseason.

Meanwhile, Hood capitalized on the starting opportunity he received Friday night and further cemented himself as one of the biggest surprises of Washington’s preseason.

Signed in January to a non-guaranteed contract after five seasons in Pittsburgh, a year in Jacksonville and an injury-shortened season in Chicago last year, Hood initially seemed little more than a training-camp body.

A first-round pick of the Steelers in 2009 (32nd overall), Hood had seen his productivity dipped dramatically the past three seasons.

However, from the start of camp, Hood steadily gained comfort in Washington’s system, and as a result, served as one of the most disruptive defensive linemen — outplaying fellow 2016 free agent addition Kendall Reyes and 2015 signing Stephen Paea — while competing for time at right defensive end.

Hood generated good pressure on the quarterback, and made plays against the run in the first two preseason games. And this week, with starting left end Chris Baker nursing a leg injury, coaches gave Hood the start.

Hood wasted little time making his presence felt, recording three tackles — two for losses — a sack and an additional hit on the quarterback. Fellow defensive lineman Ricky Jean Francois, a virtual lock to make the roster, also recorded two tackles and a sack while rotating in and out with Reyes at right defensive end.