His only ATP Tour main draw appearance came at the 2000 Grand Prix Hassan II in Casablanca, which he entered as a qualifier.

[1] At the 2000 Wimbledon Championships he made the final round of qualifying, where he was beaten in five sets by countryman Olivier Rochus.

Willems took charge of a team which had been relegated to the Europe/Africa Zone for the 2009 Davis Cup and was able to return the side to the World Group in his first year, with a 3–2 win over Ukraine in the 2009 Play-offs.

They were unable to get past the Czech Republic in the first round of the 2010 Davis Cup, but remained in the World Group with an unlikely play-off win over Australia in Cairns.

[4] He resigned as captain amid discontent in the team following Belgium's first-round World Group loss to Spain in 2011.