Second-half goals by Paul Heatley and Jordan Owens gave Crusaders victory over champions Cliftonville who had their goalkeeper Conor Devlin sent-off.
Crues winger Heatley weaved his way into the box to score with a low right-foot shot in the 60th minute.
Then, just a minute later, Declan Caddell's cross was headed by unmarked target man Jordan Owens for 2-0.
Things got worse for Cliftonville as keeper Devlin was red-carded for an off-the-ball clash with Caddell.
Crues midfielder Caddell was booked for his part in the incident by referee Robert Crangle.
It was Cliftonville's fourth defeat in the league campaign and they find themselves four points behind the new leaders Linfield.
"We have not done well at Solitude recently so to play well and get a victory against the champions is very pleasing," said Crusaders defender Paul Leeman.
"In the last three games we have defended well, but Cliftonville have top-class players and are just going through a sticky patch at the moment.
"It is only a matter of time before guys like Liam Boyce and Joe Gormley start scoring goals again.
"In my experience, it is always more difficult to retain the title than win it a first time, because everybody is out to get you.
"They have got a lot of quality - too much to continue in a poor run."