The following year, Blucas returned to television with a supporting role in the NBC event miniseries "The 60s" and a guest part on the UPN comedy "Clueless". That fall he caught an enviable break with another TV series based on a hit teen film, replacing David Boreanaz's Angel as Buffy Summers' love interest on the popular series "Buffy, the Vampire Slayer". Blucas played a Superman-like graduate student/vampire hunter, who, clad in a camouflage jumpsuit, rids the world of the evil undead by dark of night. While the gig proved a fun adventure and a dream job for an actor's exposure, Blucas soon found that not all of the diehard fans were ready for him when he stumbled upon the inevitable anti-Riley Web sites. The actor took the barbs in stride, and his character, a mysterious displaced farm boy do-gooder, soon developed his own loyal fan base. Blucas banked on his popularity translating to the big screen when he co-starred with fellow teenage heartthrob Freddie Prinze Jr. and The WB cohort Jessica Biel in Mike Tollin's sports-themed romance "Summer Catch" (2001). Supporting roles in the films "Jay & Silent Bob Strike Back" (2001), "We Were Soldiers" (2002) and "Sunshine State" (2002) followed.
In 2002, he co-starred in the Robert Harmon feature thriller, "They" and landed a major role in the acclaimed indie "I Capture the Castle" (2002) playing one of a pair of brothers who fall for the same woman (Rose Byrne). In another high-profile indie, "Prey for Rock and Roll" (2003) Blucas was cast a virginal ex-con who serves as Mr. Right for the frontwoman (Gina Gershon) of an all-female rock band. The actor was then seen in a supporting roles in the long-delayed airline comedy flop "A View From the Top" (2003) and the ill-recieved historical drama "The Alamo" (2004) before being cast as the handsome Secret Service agent who goes undercover at a college to protect a spirited Presidential offspring (Katie Holmes) in the romantic comedy "First Daughter" (2004).