With just five weeks to the election, Republican Charles D. Baker has pulled even with Governor Deval Patrick in a gubernatorial race shaped by anti-incumbent sentiment and unusually high excitement among Republican voters, according to a new Boston Globe poll. The poll results also suggest that independent Timothy P. Cahill is pulling voters equally from Baker and Patrick, raising questions about the conventional political thinking that his candidacy is undercutting Baker’s chance to defeat the governor in the Nov. 2 election. In the Globe poll, taken last week, Patrick, a Democrat, won support from 35 percent of likely voters, compared with 34 percent for Baker, a statistical tie given the poll’s margin of error. Cahill, the state treasurer who left the Democratic Party last year, continued to lag far behind with 11 percent. Green-Rainbow candidate Jill Stein got 4 percent, and 14 percent said they remain undecided. Patrick has lost ground to Baker since the Globe last surveyed voters in June, when the governor led his Republican challenger, 38 to 31 percent. Cahill, damaged by negative ads from the Republican Governors Association, is having difficulty climbing back into a race in which he was once a major contender. His standing improved slightly from June, when he won the support of 9 percent of poll respondents.