Rarely flashy, Alzner is a model of consistency. The 6-foot-2, 214-pound defenseman showed that from the early stages of his career.

Alzner made his debut in the Western Hockey League with Calgary as a 15-year-old, playing in one game during the 2003-04 season before becoming a regular in 2004-05.

He would have a standout junior career. During his four-plus seasons in juniors, Alzner appeared in 260 games with Calgary, scoring 117 points with a plus-63 rating. Along the way he helped Canada win a gold medal at the 2005 Ivan Hlinka (Under-18) Memorial Cup and gold at the World Junior Championship in 2007 and 2008. Alzner was captain of the 2008 team.

In his final year with Calgary, Alzner was named the 2007-08 Defenseman of the Year in the Canadian Hockey League (which includes the three top junior leagues). He was also named the WHL Player of the Year and Defenseman of the Year.

Selected by the Washington Capitals with the No. 5 pick in the 2007 NHL Draft, Alzner joined the Capitals to start the 2008-09 season and appeared in 30 games, but spent the majority of the season with Hershey of the American Hockey League. In the 2009 playoffs, Alzner helped Hershey win the Calder Cup, appearing in 10 games, including four in the Final against Manitoba.

Alzner started the following season with Hershey, but played 21 games with Washington and made his Stanley Cup Playoff debut in Game 7 of the first round against the Montreal Canadiens. He returned to the AHL for the remainder of the postseason and helped Hershey win a second consecutive Calder Cup.

Alzner, who earned a regular role with Washington to start the 2010-11 season, has proven to be reliable and durable. On Jan. 27, 2016, he established a franchise record for consecutive games played at 423, surpassing the mark set by Bobby Carpenter.