Shattenkirk, 28, was the one of the top players available before the 2017 NHL Trade Deadline (3 p.m. ET; March 1) and came at high cost to the Capitals, who gave up forwards Zach Sanford and Brad Malone, a first-round pick in the 2017 NHL Draft and conditional draft picks. The Capitals also received Pheonix Copley to fill their need for an experienced goaltender with Hershey of the American Hockey League.

WASHINGTON -- Not satisfied with being in first place in the NHL standings and allowing the fewest goals in the League, the Washington Capitals made a bold move to further strengthen their defense by acquiring Kevin Shattenkirk from the St. Louis Blues on Monday.

"We felt it was important to acquire another defenseman to strengthen and add depth to our blue line," Capitals general manager Brian MacLellan said in a statement. "Kevin is a skilled, puck moving defenseman who we think will help our team at even strength and on the power play."

The Capitals visit the New York Rangers at Madison Square Garden on Tuesday (7 p.m. ET; SN1, SNO, SNP, TVA Sports, MSG, CSN-DC+, NHL.TV). MacLellan said Shattenkirk is expected to arrive in New York on Tuesday and be in the lineup.

A right-handed shot, Shattenkirk is in the final season of a four-year, $17 million contract with an average annual value of $4.25 million, according to CapFriendly.com. As part of the trade, the Blues will retain 39 percent of Shattenkirk's salary and bonuses.

Video: Elliotte Friedman on the Kevin Shattenkirk trade

Shattenkirk can become an unrestricted free agent on July 1. If the Capitals re-sign him to a contract that includes the 2017-18 season, or if they advance to the 2017 Eastern Conference Final and Shattenkirk plays in at least 50 percent of their playoff games in the first two rounds of the Stanley Cup Playoffs, the Blues will receive the Capitals' second-round pick in the 2019 NHL Draft.

If Washington trades Shattenkirk on or before July 1, 2017, the Blues will receive their next available seventh-round draft pick. But if the Capitals receive a draft pick in return for Shattenkirk that is a fourth-round pick or earlier, then, instead of the Capitals' next available seventh-round draft pick, the Blues will receive the Capitals' next available draft pick two rounds later than the earliest draft pick received by the Capitals for Shattenkirk.

For example, if the Capitals trade Shattenkirk for a third-round draft pick, the Blues would receive the Capitals' next available fifth-round draft pick.

Washington (41-13-7) leads the NHL with 89 points and rank first with a 2.10 goals-against average, but there is pressure to succeed in the Stanley Cup Playoffs after the Capitals won the Presidents' Trophy last season and were eliminated in the Eastern Conference Second Round by the Pittsburgh Penguins. The Capitals have advanced past the second round of the playoffs since they made their lone Stanley Cup Final appearance in 1998 and were swept by the Detroit Red Wings.

Read: Fantasy impact of Shattenkirk trade

With his team rolling, MacLellan said on Feb. 22 that he didn't expect to make any big moves before the trade deadline.

"We're not going to mess with lines or defense pairs," he said. "If we could upgrade on the fringes, we might do it."

But MacLellan also acknowledged that depth on defense, particularly the top four, was a concern heading into the playoffs after the Capitals struggled at times defensively against the Penguins in the playoffs last season.

Acquiring Shattenkirk addresses that need. The Penguins and the Rangers were reportedly among the other teams pursuing Shattenkirk. By trading for him, the Capitals prevented him from going to one of their Metropolitan Division rivals.

Video: STL@WPG: Shattenkirk makes nifty move to notch goal

Shattenkirk has 42 points (11 goals, 31 assists) in 61 games this season and was a key part of the Blues power play, with seven goals and 13 assists. He has 284 points (66 goals, 218 assists) in 471 NHL regular-season games in seven seasons with the Blues and Colorado Avalanche.

Shattenkirk was selected by the Avalanche in the first round (No. 14) of the 2007 NHL Draft. He was traded to the Blues on Feb. 19, 2011, during his rookie season.

The Capitals picked Sanford, 22, in the second round, No. 61, of the 2013 NHL Draft. Sanford left Boston College after his sophomore year to sign a three-year entry-level contract on July 11, 2016. Although the 6-foot-4, 203-pound Salem, Massachusetts native played center in college, he's played left wing and right wing for the Capitals and Hershey in the American Hockey League.

In 26 games with the Capitals this season, he had three points (two goals, one assist). His first NHL goal was the game-winner in a 6-4 victory against the Anaheim Ducks on Feb. 11. Sanford also had 16 points (11 goals, five assists) in 25 games with Hershey.

Malone, 27, had 20 points (seven goals, 13 assists) in 52 games with Hershey this season.

Copley, 25, began his professional career with the Capitals organization playing for Hershey and South Carolina in the ECHL before being traded to the Blues, along with forward Troy Brouwer and a third-round draft pick in 2016, in the deal that brought right wing T.J. Oshie to Washington on July 2, 2015.

"We are also pleased to welcome Pheonix back to the organization," MacLellan said. "We feel his addition solidifies our goaltending tandem in Hershey."