Syers had managed just five league goals this season heading into his side's clash with Portsmouth, but he almost doubled his tally in a thumping 5-1 win.
Also on the scoresheet were Sam Winnall and Paddy Madden, with Portsmouth's Michael Drennan heading home a late consolation for the visitors.
The win meant that Scunthorpe joined Chesterfield at the summit, with Paul Cook's side shocked 1-0 by Wycombe Wanderers.
And they were further boosted by rivals Oxford United's failure to overcome Morecambe, for whom Robbie Threlfall netted a last-gasp leveller to cancel out David Connolly's 13th-minute opener.
Fifth-placed Fleetwood slipped to a 1-0 defeat at Mansfield thanks to Matt Rhead's winner, while Southend United, who are seventh and in the final play-off spot, could only manage a goalless draw at York City.
Elsewhere, Danny Mayor's injury-time effort earned Bury a 1-0 win at AFC Wimbledon, Newport County were edged out 1-0 by Cheltenham Town as Ashley Vincent got the only goal and Plymouth Argyle grabbed all three points with a 2-1 win over Dagenham and Redbridge.
