Wallace re-signed with Portland on December 6, 2012. In summer 2014, Wallace was sent on loan to USL Pro club Arizona United to regain match fitness after returning from injury.
Wallace returned to the Portland Timbers at the beginning of the 2015 season. He served as a regular starter all of the regular season. In the 2015 Audi MLS Cup playoffs, Wallace played a vital role in the team's success, scoring a goal against Sporting Kansas City in the knockout rounds. They went on to win that game in a penalty shootout 7-6 in what was the longest penalty shootout in MLS Cup playoffs history. The Timbers would go on to win the Western Conference Championship against FC Dallas and enter their first ever MLS Cup Final. Wallace came up big in the final, scoring what would go on to be the game winner in the 7th minute. The final score was 2-1.
During his first season in Portland, Wallace established himself as a starter at left midfield for the expansion club. His efforts earned him a call to represent Costa Rica in September. He made his international debut on September 2, 2011 at the Home Depot Center in Carson, California, and scored the only goal in a 1-0 victory over the United States. As of December 2014, Wallace has earned a total of 17 caps, scoring 3 goals. He represented his country in 3 FIFA World Cup qualification matches.