January 1999, saw West Ham lose 1–0 in an FA Cup tie against his hometown club, Swansea City. Hartson played 73 times and scored 33 goals for the east London club. Wimbledon Hartson joined Wimbledon in January 1999, becoming the club's most expensive signing ever at £7.5m. His time with the Dons was marred by injury, though he still managed a respectable goal tally, first in the Premier League, then the First Division following the club's relegation in 2000. Proposed moves to Rangers, Tottenham and Charlton fell through due to doubts over the player's fitness. Hartson instead joined Coventry City on a pay-for-play deal in February 2001. Coventry City Hartson made his Coventry debut against former club West Ham on 12 February 2001. He went on to score six goals in twelve league games, including a brace in a defeat to Manchester United at Old Trafford. However, despite his efforts Coventry were relegated from the Premier League at the end of the season. Celtic In August 2001, Hartson joined Celtic in a £6m transfer. He made his debut on 4 August 2001, coming on as a substitute in a league match away at Kilmarnock. He scored his first goals for Celtic when he scored a hat-trick in a 5–1 win over Dundee United on 20 October 2001. At the end of his first season at Celtic he helped them win the Scottish Premier League title. In December 2002, Hartson scored as Celtic were beaten 2–1 in the away leg of their third round UEFA Cup tie against Celta Vigo. However, with the aggregate score 2–2, Celtic progressed on the away goals rule. This was the first time that Celtic had remained in European competition after Christmas since 1980. In March 2003, Celtic faced Liverpool in the UEFA Cup at the quarter final stage, drawing 1–1 in Glasgow. In the return leg at Anfield, Hartson fired the club's goal of the season with a strike past Jerzy Dudek into the top corner from over 25 yards out. Celtic won this match 2–0, progressing to the semi-final. After scoring the winning goal against Rangers at Ibrox in late April Hartson was plagued by a back injury which meant he missed the rest of the season, including the 2003 UEFA Cup Final. Nevertheless, he had played a major role in getting Celtic all the way through the tournament, with his goals in Liverpool