Glasgow club, and threatened the League with legal action to gain membership. The restructuring of the league in the early part of the 21st century eventually resulted in both Celtic clubs gaining admission to the Irish Football League Second Division for the 2002–03 season. In 2003 the club closed their town centre ground Grattan Park and relocated to share Oxford United's ground on the edge of Lurgan at Knockramer Park, which offered better facilities. Promotion to the Intermediate League First Division was achieved in 2006–07, but in 2008 the club failed to meet the criteria for a place in the new IFA Championship, and found itself in the IFA Interim League for the 2008–09 season. They successfully made the necessary improvements to gain admission to the newly formed third tier, IFA Championship 2, for the 2009–10 season. After seven seasons of consolidation in Championship 2 with occasional flirts with relegation, Celtic surged to the 2014–15 NIFL Championship 2 title, achieving promotion to the national second tier, Championship 1. On the back of their title success the previous season, Celtic pulled off one of the local game's biggest giant-killing acts of the 21st century. After reaching the quarter-finals for the first time ever in the 2015–16 Irish Cup, Celtic were drawn to face senior NIFL Premiership side and beaten Irish Cup finalists the previous year, Portadown away at Shamrock Park. Celtic stunned the Ports by taking a 2–0 lead after 54 minutes. However, Portadown came back into the match after 70 minutes with two goals of their own to level the score at 2–2. However, Lurgan Celtic had the last say, and scored a last-minute penalty to win 3–2 and cause a major upset by eliminating Portadown, and reaching the semi-finals of the cup for the first time in the club's history. The match was also notable as Portadown's final match under the management of Ronnie McFall. After the match, the Portadown manager resigned, ending his reign at the club after 29 years. In the Irish Cup semi-final they were defeated 3–0 by Linfield with Aaron Burns scoring a hat-trick. Despite the achievement of reaching the Irish-Cup semi-finals, manager Colin Malone resigned at the end of the 2016-17 season and the club endured a period of instability. The appointment of Brendan Shannon as Celtic player-manager could not prevent a serious downturn in results, and Shannon left halfway through the 2017-18 season,