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.
Max Kretzschmar converted from the penalty spot to earn Wycombe a crucial three points that leaves them five ahead of second-bottom Torquay United.
For Torquay, a 1-0 home defeat to Accrington Stanley, in which Kal Naismith grabbed the winner, was made worse by bottom side Northampton Town beating play-off-chasing Hartlepool United 2-0.
Mathias Kouo-Doumbe and Brennan Dickenson found the net as basement club Northampton moved level on points with the side directly above them.
In the race for promotion, meanwhile, Rochdale enhanced their claims on the third automatic spot with a 1-0 win at Exeter City, Jamie Allen scoring the decisive goal.
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.
