DENVER, Colorado: It was not a good night for Mitt Romney: first he was trounced by Rick Santorum in three Republican state polls, and then he was glitter-bombed at an event where he congratulated his rival.

What had been expected to be a party in Denver, where polls had predicted he would comfortably win the Colorado caucus, turned into an evening the former Massachusetts governor would probably rather forget.

A Public Policy Polling (PPP) survey only last weekend had predicted that Romney would win 40 percent of the vote in the Centennial State, against 26 percent for Santorum, 18 for Gingrich and 12 for Ron Paul.

The first sign that something was not going well came when the Denver event Tuesday night -- billed as a party for supporters to greet the caucus results with Romney and his family -- was late in starting.

Then one of his sons, Josh, was brought on, telling the small audience that he had had to step into his mother's shoes to introduce his father.

Romney came on and immediately acknowledged that the results were "too close to call," but that he was confident he would end the evening in first or second place.

But no sooner had he finished his brief address for the cameras and begun the usual round of hand-shakes with supporters, then someone appeared to spray glitter in his face.

Slow-motion video of the incident showed a clearly startled Romney register shock, as a blue-looking substance was sprayed at him, apparently by one of the people whose hands he was shaking.

As Secret Service bodyguards -- who have only been accompanying Romney since last week -- quickly stepped in, the Republican frontrunner stepped back, looking uncertain and clearly anxious.

He was quickly whisked further along the handshake line, and within a second or two had regained his composure and resumed the glad-handing -- as live television showed a young man bundled out of a side door by security.

In his remarks, Romney congratulated the Christian conservative Santorum on his wins in Minnesota and Missouri, and his good showing -- which barely an hour later proved to be victory -- in Colorado.

"This was a good night for Rick Santorum. I want to congratulate Senator Santorum," he said, while insisting: "I expect to become our nominee with your help."

Results published by the Colorado Republican Party gave Santorum a clear win of 40 percent, ahead of Romney's 35 percent. Gingrich came in third with 13 percent, followed by Paul with 12 percent.

Long-time frontrunner Romney appeared to have cemented his lead with resounding wins in Florida and Nevada last week, but Santorum's surprise hat trick has added another twist to the roller-coaster race.

"Tonight was a victory for the voices of our party, conservatives and Tea Party people, who are out there every single day in the vineyards building the conservative movement in this country," Santorum said in his victory address.

The Republican establishment hopes the contest will be over well before the August 27-31 convention in Tampa, Florida, avoiding a bitter battle that could hurt the eventual nominee's chances against Democratic President Barack Obama.