Celtic blew open the title race with this narrow victory over their greatest rivals. The win rounded off a good four days for the visitors with a UEFA Cup Final to come in May.
Goals by Alan Thompson, from the penalty spot, and John Hartson in the first half won this match for Celtic and reduced the gap on Rangers to five points with a game in hand.
Rangers threatened a comeback early in the second half with Ronald de Boer's header, but they found it too difficult to breach a Celtic defence where Bobo Balde and Joos Valgaeren were rock-solid.
The home side were made to rue wasting some early chances. Claudio Caniggia lobbed Rab Douglas when put through by de Boer's pass but was wide of the target.
Then Lorenzo Amoruso headed over from close range before de Boer pulled his shot wide from good position.
Celtic gradually forced their way back into the match and Jackie McNamara's curling free-kick from the halfway line was left by everyone and spun back off the post much to the relief of Stefan Klos.
The visitors took the lead with a soft penalty award when Amoruso was adjudged to have brought down Hartson on the edge of the area. Thompson made no mistake, drilling his spot-kick low past Klos.
Celtic increased their lead with a well worked goal, Hartson released Didier Agathe down the right wing and after skipping past Peter Lovenkrands his cut-back was touched on by Henrik Larsson, allowing Hartson to stroke the ball home from 12 yards.
Rangers were fired up from the start of the second half and Fernando Ricksen and Amoruso both went close before de Boer scored.
Lovenkrands' pass found Arthur Numan whose cross was headed home powerfully by de Boer at the far post.
The home side tried all they knew in search of an equaliser, but other than a couple of efforts from de Boer and Amoruso they were unable to find a way through.
Celtic nearly increased their lead near the end, but Klos did well to block Larsson's shot.