The first pitch of Matt Riley's major league career was smoked for a triple. His sixth pitch brought home his first earned run. His 15th and 65th pitches were preceded by balks. And with his 69th pitch, Riley issued his fourth walk, handed the ball to Manager Ray Miller and walked slowly back to the Baltimore Orioles' dugout.

The best thing that can be said about Riley's major league debut, which was met with unbridled excitement within the organization, is that it is over. Doomed by an egregious lack of command and given little help by his defense, the 20-year-old lefty failed to make it out of the third inning tonight in the Orioles' 6-5 victory over the Minnesota Twins.

"I'm glad to get it over with," said Riley, whom the Orioles envision in their starting rotation next year. "It was just a shaky outing. Whether it's my first start or my 50th, I hate to pitch like that."

"I don't really want to judge his stuff," Miller said. "It looked like he was trying to guide the ball. It's good to get this out of the way."

The Orioles' most important game since the all-star break took place before a paltry crowd of 9,903 in the cavernous Metrodome between two fourth-place teams. But despite the low-key setting, which the Orioles preferred to a packed Camden Yards, Riley appeared animated and fidgety, never comfortable.

"I really had no rhythm," he said. "I wasn't nervous, but I had trouble getting relaxed."

And like the Orioles' season itself, Riley's debut failed to live up to expectations. His first pitch wound up as a triple, when Denny Hocking's liner into left-center clanged off the glove of center fielder Eugene Kingsale. It did not get much better from there.

The next batter, Brent Gates, lofted a sacrifice fly, which Kingsale snagged with a diving catch. By the time the inning ended, Riley had given up a walk and a stolen base and committed a balk; and catcher Charles Johnson and pitching coach Bruce Kison had made a combined four trips to the mound.

"We were just trying to walk him through," Miller said. "Remember, he's only 20."

Riley's second inning was his best. Chad Allen led off with a double, moved to third on a groundout and scored on an infield single that short-hopped rookie second baseman Jerry Hairston. Twins shortstop Cristian Guzman swung through a 92-mph fastball -- Riley's hardest of the night -- for Riley's first major league strikeout.

But by the third, Riley began to look completely lost. He opened the inning by walking Gates, the first of three walks in the inning. The inning also included a single off the glove of rookie shortstop Jesse Garcia.

In all, Riley threw only 31 strikes in 69 pitches. More tellingly, he threw first-pitch strikes to just three of the 15 batters he faced, and fell behind either 2-0 or 3-1 a total of nine times. Other than two change-ups, everything he threw was fastballs or curves.

"I've had a lot of trouble my last three starts finding my rhythm," he said. "I don't have the smooth delivery I had earlier in the year."

Still, Riley's debut was not a disaster. His performance -- two earned runs allowed in 2 2/3 -- did not cost the Orioles the game. Led by Hairston (2 for 5 with a homer and two RBI) and Brady Anderson (3 for 4 with a homer and two runs scored), the Orioles rallied from a 4-3 deficit to complete a three-game sweep of the Twins and win the season series 8-1.

Despite the fact that Riley was making arguably the most important pitching debut the organization has seen since Mike Mussina on Aug. 4, 1991, the Orioles have taken great pains to insulate him from high expectations, and perhaps now it is clear why. Having breezed through the Orioles' minor league system in only 16 months, Riley has not known much adversity in his professional career.

No determination has been made yet on Riley's next start, but there is growing concern within the organization about overusing his arm. By the time he arrived in the Orioles' clubhouse, Riley already had thrown 177 1/3 innings this season. Tonight, his fastball stayed mostly in the 88- to 89-mph range, down a couple of miles from usual.

"His velocity wasn't what I expected," Miller said. ". . . But he wasn't afraid. He was ticked off at himself when he came out of the game."

Orioles Notes: Second baseman Delino DeShields had sensory nerve entrapment diagnosed in his right quadriceps, which has been causing him discomfort and a loss of explosiveness. DeShields will play the rest of the season, then have an outpatient procedure to "release" the nerve, according to Orioles trainer Richie Bancells. . . .

Mussina (bruised right shoulder) threw three simulated innings in the bullpen before the game, and is scheduled to start Tuesday for the first time since Aug. 22. . . . Albert Belle's RBI single tonight gives him his eighth straight 100-RBI season.