CHICAGO- An Illinois Democrat who won his party's nomination on Tuesday to campaign for Barack Obama's vacant Senate seat struck a populist tone, attacking his Republican opponent as part of the Washington establishment.

Democratic state treasurer Alexi Giannoulias said the voter discontent that helped Republicans to a surprise victory in last month's Senate race in Massachusetts would work against Representative Mark Kirk, who easily won the Republican primary.

There is voter anger at Washington, D.C., and Washington, D.C., is ignoring everyday working-class families. Congressman Mark Kirk for the last 10 years has been steeped in D.C. politics and will have to answer for that, Giannoulias said.

Kirk, a 50-year-old five-term congressman with a moderate voting record, urged an end to the Democrats' stranglehold on Illinois politics.

The people of Illinois now see the arrogance of a one-party state, Kirk told supporters.

Banking scion Giannoulias, 33, beat back two main challengers to earn a shot at replacing Senator Roland Burris, who did not run. Burris was appointed to Obama's former seat by former Governor Rod Blagojevich, who was removed from office a year ago and faces trial on corruption charges in June.

One poll showed Giannoulias edging Kirk in November, a far cry from Obama's resounding victory over Republican John McCain in the 2008 presidential election, when the Democratic candidate won 62 percent of the vote.

Illinois' primary was the first in the nation ahead of the November 2 mid-term congressional elections, and analysts searched for signs of voter dismay with Democrats in the White House and Congress.

Discontent with incumbents threatened Democratic Illinois Governor Pat Quinn, who appeared to have eked out a narrow victory over Comptroller Dan Hynes. Quinn declared himself the winner.

The crowded race for the Republican nomination for governor came down to a tight contest between two lesser-known state legislators, including conservative Bill Brady.

(Reporting by Andrew Stern; Editing by Paul Simao.)