(CNN) -- Rangers have been knocked off top spot in the Scottish Premier League after slumping to a shock last-gasp 1-0 home defeat by Inverness Caledonian Thistle.
Walter Smith's side are now three points behind Glasgow rivals Celtic, who went back to the summit after leaving it late to win 2-1 at Kilmarnock.
Meanmwhile, at Ibrox, Ian Black kept his nerve to convert from the penalty spot in the final minute for one of the biggest surprise results of the Scottish season.
Veteran defender David Weir fouled David Proctor in the area in the final minute, an offense for which he was sent off, allowing Black to secure the points for the visitors.
Meanwhile, a Scott McDonald double against Kilmarnock took Celtic clear of their neighbors and on course for their fourth title in a row.
The defending champions dominated the first half but Danny Invincible's volley after 36 minutes cancelled out his fellow Australian's opener 10 minutes earlier.
Celtic huffed and puffed at times after the break but with 10 minutes remaining McDonald struck with a wonderful solo goal to put the Parkhead side back on top.