Rex Ryan has vowed to build a bully in Buffalo. His first challenge is no pushover, however.

The colorful coach leads the Bills into their most anticipated season in years Sunday against the Indianapolis Colts, who enter 2015 with the highest expectations possible.

Ryan's unabashed optimism and larger-than-life persona has breathed new life into what has been one of the NFL's most moribund franchises over the past decade. He unsurprisingly expressed confidence during January's introductory press conference that the Bills' 15-year postseason drought - the NFL's longest active streak - would soon be over.

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"I'm not going to let our fans down," he said. "I know it's been 15 years. Well, get ready. We're going."

Ryan has the track record to back up those boasts, having led the New York Jets to the AFC championship game in the first two seasons of an eventful six-year run that ended after last season. He's got something to build on as well after the 2014 Bills posted their first winning season since 1999, the last time Buffalo (9-7) made the playoffs.

''That's the expectation in here, upstairs and in town,'' defensive tackle Kyle Williams said. ''When we go out on Sunday, we're not just going out there to compete, we're going out there to win.''

Simply reaching the playoffs would be viewed a disappointment for Indianapolis (13-6) after it reached last season's AFC title game behind one of the most productive offenses in the league. Though a 45-7 loss to New England in the infamous "Deflategate" game showed there's still work to be done, the Colts believe they're ready to take another step forward in the fourth year of the Andrew Luck/Chuck Pagano regime.

"The inside expectations, and I've said this since Day One, they've always been high," Luck told the Colts' official website. "They've always been get to the playoffs and give yourself a chance to go win a Super Bowl. That hasn't changed."

Luck's emergence as a franchise quarterback has justified those championship aspirations. The 2012 No. 1 overall pick threw for a league-high 40 touchdowns and broke Peyton Manning's single-season team record with 4,761 passing yards in directing the third-ranked offense in the NFL.

Though receiver Reggie Wayne wasn't retained, two other accomplished veterans - running back Frank Gore (1,106 rushing yards, four touchdowns with San Francisco) and receiver Andre Johnson (85 catches, 936 yards, three TDs with Houston) - were brought in to join Luck and dynamic wideout T.Y. Hilton (82 catches, 1,345 yards, seven TDs) to join what could be an even more prolific attack than last year.

''I am just here to try and take full advantage of it,'' Johnson said. ''That was a big part of my decision this offseason when I became a free agent, going to a place that had an established quarterback and a great quarterback.''

Hilton, signed to a five-year, $65 million extension last month, is expected to play despite sustaining a concussion in the third preseason game.

The Bills will hang their hopes on a defense that Ryan has already proclaimed will be the league's best. The unit wasn't far off last year, topping the NFL with 54 sacks while finishing third in takeaways (30) and fourth in yards allowed (312.2 per game).

Ends Mario Williams and Jerry Hughes and All-Pro tackle Marcell Dareus recorded double-digit sack totals last season, though Dareus is suspended for the opener for violating the NFL's substance-abuse policy. Starting cornerback Leodis McKelvin (ankle) was placed on the reserve/non-football injury list, meaning he will miss at least the first six weeks. Rookie Ronald Darby is likely to be tested in his place.

''I'm confident he'll do a good job for us,'' Ryan said of Darby.

Buffalo's LeSean McCoy (1,319 rushing yards, five touchdowns with Philadelphia in 2014) says he's "ready to go'' after the marquee offseason addition missed nearly all of the preseason with a strained left hamstring. The 2013 NFL rushing champion will be counted on to ease the burden on Tyrod Taylor in the quarterback's first career start.

Taylor attempted only 35 passes in four seasons with Baltimore but beat out veteran Matt Cassel and former first-round pick E.J. Manuel with a solid preseason in which he rushed for 108 yards on 11 carries. Those scrambling skills should fit well in what's expected to be a run-based offense centered around McCoy and orchestrated by new coordinator Greg Roman, who coaxed four straight 1,000-yard seasons out of Gore in San Francisco.

The Colts were gashed for 177 rushing yards by New England in the AFC championship and will be starting a pair of rookies, Henry Anderson and David Parry, along the defensive line. They're hopeful that Robert Mathis, the NFL leader with 19 1/2 sacks in 2013, will return from a torn Achilles that sidelined him all last season.

The teams are meeting for the first time since the Colts won 20-13 at home in 2012. Indianapolis has taken seven of the past eight matchups but lost 30-7 in its last visit to Ralph Wilson Stadium in the 2010 season finale.