Alex Fishback opened the fourth inning with a double, but it appeared the Tomcat would be stranded on base as Guelph retired the next two batters.
However the Tomcats had some two out magic.
After Brendan Johnston drew a walk, Fishback scored on an Alex Pettipiece single, tying the game. A Josh Hare double and Xavier Jamieson single drove in three more runs.
The Tomcats added a run in the fifth inning on a two out RBI single from Johnston, scoring Will Pollard who had tripled.
Arthur Kowara's three-run homer pulled the Silvercreeks to within a run, at 6-5, in the home side of the fifth.
Pettipiece, Hare and Pollard, each finished with two hits. Henderson drew two walks and scored twice.
St. Thomas pitchers combined to strike out 13 batters over seven innings, while giving up eight hits and three walks.
The Tomcats are 5-2 overall.
Four teams, St. Thomas, Guelph, Welland and Brantford, are tied for first place at 3-2, in the Junior IBL standings.
St. Thomas begins a busy weekend of five games in three days, entertaining the Silvercreeks, Friday, 7:30 p.m., at Emslie Field.
It's exhibition action Saturday when the Windsor Selects visit Emslie Field for a twin bill starting at noon.
On Sunday, the Stratford Nationals are in town for two league games.
Free admission to all games.
St. Thomas hosts an eight team 22U Ontario Baseball Association championship, July30-August 1, at Emslie and Cardinal fields.
The Tomcats face the Ilderton Red Army, out of the Southwestern Senior League, Thursday, August 5, at Labatt Park, in London. First pitch 7 p.m.