Hillary Clinton has a huge lead over Donald Trump in one of the most consequential swing states

Hillary Clinton. Alex Wong/Getty Images

A poll released Thursday showed Hillary Clinton with a massive lead over Donald Trump in Pennsylvania — a state both presidential candidates are zeroing in on.

The Suffolk University poll showed Clinton with a 9-point lead over Trump in the Keystone State as the Democratic National Convention takes place in Philadelphia. When Libertarian nominee Gary Johnson and Green Party nominee Jill Stein are included, Clinton's lead remains 9 points.

Knowing the importance of the battleground state, Trump and his running mate, Gov. Mike Pence of Indiana, stopped in Scranton, Pennsylvania, on Wednesday for a campaign event. After the DNC wraps up Thursday, Clinton will be holding rallies alongside her running mate, Sen. Tim Kaine of Virginia, in Philadelphia and Harrisburg on Friday and in Pittsburgh on Saturday.

The poll was one of few that provided encouraging news for Clinton as Trump experienced a big bump after last week's Republican National Convention in Cleveland. The Republican nominee leads Clinton in the national average on RealClearPolitics by 0.9 points — his largest lead in the coveted polling average all cycle.

But to win in the fall, Trump will almost certainly need to flip Pennsylvania, Ohio, and Florida from their 2012 blue results.

The poll also provided encouraging results for Democratic Senate nominee Katie McGinty, who is challenging Republican incumbent Pat Toomey. McGinty held a 7-point lead over Toomey in the poll, her largest lead over Toomey in any poll posted to RealClearPolitics.

The Suffolk poll has proved accurate in recent Pennsylvania Senate contests. The final Suffolk poll ahead of the 2010 election between Toomey and Democratic nominee Joe Sestak showed a 5-point advantage for the Pennsylvania Republican, who went on to win by 2 points. In the final poll ahead of the 2010 Democratic primary, Suffolk predicted a 9-point upset for Sestak over longtime incumbent Arlen Specter. Sestak won by 8 points.

Suffolk polled 500 likely voters via live telephone interviews, and the margin of error was 4.4 points. It was conducted from Monday to Wednesday, right as the four-day DNC was taking place in the state.

In the most recent Pennsylvania poll posted to RealClearPolitics before Thursday, conducted by NBC News/The Wall Street Journal, Clinton was found to hold the same 9-point advantage over Trump.