Anderson and Wright suffered a surprise first round 5–2 defeat to Singapore at the World Cup. Gary ended the 2017 season with a loss to finalist Phil Taylor in the quarter-finals of the 2018 World Championship, failing to reach the finals for the first time in 4 years. With Rob Cross breaking into the top 3 in Order of Merit with his World Championship victory over Taylor, Anderson would play the 2018 season ranked 4th in the world. This would queue him up for a series of semi-finals matches against Michael van Gerwen, the first of which would be a 5–11 loss in the Masters. Anderson returned 2 weeks later to win the 4th UK Open Qualifier and enter the UK Open as the 6th seed. Having not reached the final since his 2010 loss to Taylor, Anderson reached the final for a second time to defeat Corey Cadby 11–7. Just a week later, Anderson followed up with back to back victories in Players Championships 3 and 4. In the 2018 Premier League, Anderson had an 8–5–3 (W–L–D) record to finish 3rd in the league table and reach the playoffs for the 5th year straight, but would fall to Michael Smith in the semi-final. Nevertheless, Gary would turn around two days later to win his third Players Championship title of the year. Another two weeks later, Anderson would join Peter Wright for the fourth time to represent Scotland at the 2018 World Cup. With the pair having only lost one set before the finals, they fell to the reigning champions, Michael van Gerwen and Raymond van Barneveld of The Netherlands with MVG's 4–0 defeat of the Flying Scotsman. Anderson kicked off the second half of the year with an 8–4 victory over Rob Cross in the final of the US Darts Masters where he hit the tournament high checkout of 164 in the final leg. The following week, his World Series success would come to an end after a first round defeat in the Shanghai Darts Masters. His form was soon to return in the World Matchplay where he hit a ₤45,000 nine-dart finish against Joe Cullen in the semi-finals. With a defeat over Cullen and Jeffrey de Zwaan, who had beaten other two-time world champions Michael van Gerwen and Adrian Lewis in the first two rounds, Anderson met Mensur Suljović in the final. In the longest match in Matchplay history, Anderson defeated Suljović 21–19 in the best of 35 match with the stipulation that the game must be won by 2 clear legs.