Tyler Chatwood's extra work on offspeed pitches during spring training made a huge difference Saturday. Chatwood pitched 5 2/3 perfect innings before Chris Marrero's single and finished with a two-hitter for the Colorado Rockies in his first big league shutout, a 5-0 win over the San Francisco Giants. ''The first two outings I didn't feel like I threw the ball bad, but I gave up homers that killed me,'' Chatwood said.