Syers, who helped Doncaster Rovers win promotion to the Championship last season, struck twice either side of half-time as the Iron came from behind to halt a barren five-match run.
Pompey's first flowing move of the match culminated with Craddock heading his maiden Blues goal from a Ricky Holmes cross.
Portsmouth's lead lasted only four minutes, though, with Syers equalising at the far post after Andy Dawson's corner found its way through the six-yard box.
Portsmouth twice hit the Scunthorpe woodwork but Carson twice made fine saves to deny the visitors.
- Sports & Recreation
- Tom Craddock
- Doncaster Rovers