The 21-year-old right-hander allowed an unearned run on one hit over seven innings before the Chattanooga Lookouts dropped a 3-2, 14-inning decision to the West Tenn Diamond Jaxx.
De La Rosa dropped a throw at first base that enabled Johan Limonta to reach leading off the second. After Guillermo Quiroz reached on third baseman Corey Smith's miscue, De La Rosa surrendered a one-out RBI single to Leury Bonilla.
The native of the Dominican Republic settled in after that and got help from left fielder Elian Herrera, who threw a runner out at third after De La Rosa issued back-to-back walks to open the fourth.
De La Rosa struggled with his control throughout, issuing four free passes while striking out four. But he still has not yielded an earned run over 18 innings in three starts since the Dodgers promoted him from Class A Great Lakes.
The non-drafted free agent began the Midwest League season in the bullpen and went 1-1 with six saves and a 4.45 ERA in 10 games. But he took off after joining the starting rotation in late June, going 3-0 with a 1.67 ERA in four outings.
Overall, De La Rosa is 5-1 with a 2.44 ERA in 17 games, including eight starts. He was in line for another win before West Tenn took advantage of the fourth of the Lookouts' five errors to tie the game in the ninth.
Carlos Peguero put the Diamond Jaxx in front in the 14th with his 20th homer.