He said he threw a pitch "that was a little bit uncharacteristic of me. Right then and there, the tire deflated."
The defending NL West champion Dodgers had started the regular season with a two-game sweep of the Arizona Diamondbacks in Sydney.
Ryu got the start after reigning NL Cy Young Award winner Clayton Kershaw was scratched due to a swollen back muscle and then placed on the 15-day disabled list for the first time in his seven-year career.
In a scheduling quirk, the left-hander started consecutive regular-season games. He made his season debut a week earlier, when the Dodgers beat the Diamondbacks in their second game in Australia.
Ryu retired 16 in a row from the second inning until one out in the seventh. He then walked rookie Tommy Medica, who was then erased in a 3-6-3 double play.
Ryu allowed three hits, struck out seven and walked three.
The Dodgers grabbed the lead on a nice piece of hitting by Carl Crawford with two outs in the fifth.
Crawford went the other way with an 0-2 pitch from Andrew Cashner, hitting it over third baseman Chase Headley to bring in Dee Gordon from second. Gordon had reached on a walk and advanced when Cashner fielded Ryu's bunt and forced A.J. Ellis at third.
Cashner allowed four hits in six innings. He struck out five and walked two.
NOTES: The Padres renamed the broadcast portion of the press box the Jerry Coleman Broadcast Center in memory of the Hall of Fame broadcaster who died on Jan. 5 at 89. His widow, Maggie, and daughter, Chelsea, threw out the ceremonial first pitches. ... Sunday night's attendance of 45,567 set the Petco Park single-game record. ... Padres manager Bud Black said LF Carlos Quentin's time on the disabled list will go beyond April 10, when he'd be eligible to be activated. He was placed on the DL on Saturday, retroactive to March 25, with a bone bruise in his left knee. Quentin was hurt diving for a ball in a spring training game. ... Monday is an off day. Tuesday's scheduled starters are Zack Greinke for Los Angeles and Ian Kennedy for San Diego.