A two-run double by Rafael Furcal gave Los Angeles only their second lead in the series, 3-2, but Guillermo Mota, taking over for starter Hiroki Kuroda, gave it back in the bottom of the inning.
After Kemp's single in the 10th, Jonathan Broxton, who blew the save the night before in the ninth inning, McDonald got credit for the win and Broxton recorded his 24th save.
Asked about the blown save the night before, Broxton said, "It's just one save. We're going to give them up like I did last night, a little cheap broken-bat single. As a reliever you've got to bounce back the next day and be ready to go."
Kuroda indicated that he had overcome his early-season injury, working six inning and allowing the charging Cardinals only four hits and single runs in the first and fourth innings.
Matt Holiday dropped a soft single into left field to score Albert Pujols with the first run but there was nothing soft about Holliday's home run to deep right field in the fourth.
Los Angeles had tied the game in the second when Casey Blake doubled with one out and Kemp singled to left to drive him in with two out.
Neither team could mount much of an offense from the fourth inning until the seventh when Brad Ausmus, giving Russ Martin a day off, singled to center, went to second on a wild pitch, and Juan Pierre, hitting for Kuroda, beat out an infield hit to short.
Rafael Furcal sliced a shot down the left field line that scored both Blake and Pierre to give the Dodgers short-lived 3-2 lead.
The Dodgers had little time to enjoy the lead. Mota served up a leadoff home run to Rick Ankiel in the last of the inning to tie the game
Blake singled to open the eighth and then was thrown out stealing. Television replays seemed to indicate he was safe, and had he been the Dodgers would have taken he lead when Kemp singled with one out later in the inning.
St. Louis, with a fourth-straight capacity crown attempting to boot them home, almost put the game away in the last of the eighth.
Mota served up a leadoff double to pinch-hitter Nick Stavinoha and manager Joe Torre was quick to replace him with Hong-Chih Kuo, who was appearing in his second straight game. He was bunted to second and Kuo fanned the pesky Ryan Ludwick.
With the Cardinals' twin towers, Pujols and Holliday coming up with the lead run at third base, Torre opted to walk both of them intentionally, an unconventional moved that he would explain after the game as, "lose by one, lose by four, what's the difference."
But Kuo had little thought of losing this one and blazed three fastballs by Ankiel, the last two clocked at 95, to choke off the threat.
Both teams went quietly in the ninth. Rookie James McDonald, inserted into the important game in the ninth inning because the 15-inning game the night before burned up most of the bullpen, worked a 1-2-3 ninth inning and earned the win.
In the top of the 10th, however, Andre Ethier fell behind 0-2 but coaxed a walked and Blake dropped one of his patented looping singles into right field. A wild pitch moved both runners up a peg and James Loney fanned before Kemp picked up his 58th and 59th runs batted in with a single.
Broxton walked former Dodger Joe Thurston in the bottom of the inning but then retired three in a row, including Pujols on a tap back to the mound for the final out.
Kemp had three hits and three runs batted in. Blake had four hits and scored twice to lead the Dodgers who out-hit the Cardinals 12-6. Manny Ramirez was 0-for-5 in the game and 3-for-18 in the series without knocking in a run. He is also 4-for-26 in his last six games.
The Cardinal fans greeted him with boos before each at-bat.
Los Angeles was 4-for-11 with runners in scoring position after recording an ugly 4-for-25 in the first four games.
"That was just a terrific series," Cardinals manager Tony La Russa said after the game. "We made a lot of good things happen and had a great chance tonight. They're a very good club."
The Dodgers hope for another series in St. Louis this season, which would mean they would be in the playoffs. Much like jumping out of the frying pan into the lion's den, they flew on to Atlanta for three more important games.
Tonight, RHP Jason Schmidt (3-5, 4.57) and RHP Tommy Hanson (5-1, 2.95)
Saturday, LHP Randy Wolf (5-5, 3.43) and Derek Lowe (10-7, 4,29)
Sunday, RHP Chad Billingsley (10-6, 3.95) and RHP Jair Jurrjens (9-7, 2.69).
Score by Innings Los Angeles 010 000 000 0-5 St. Louis 100 100 100 0-3 Los Angeles ab r h bi ave Furcal ss 5 0 1 2 .265 Hudson 2b 4 0 0 0 .287 Ramirez lf 5 0 0 0 .317 Ethier rf 3 1 0 0 .265 Blake 3b 5 2 4 0 .283 Loney 1b 5 0 0 0 .289 Kemp cf 5 0 3 3 .316 Ausmus c 5 1 2 0 .313 Kuroda p 2 0 1 0 .143 Pierre ph 1 1 1 0 .316 Mota p 0 0 0 0 .000 Kuo p 0 0 0 0 .000 Loretta ph 1 0 0 0 .225 Mcdonald p 0 0 0 0 .000 Broxton p 0 0 0 0 .000 --------------------------------- Totals 41 5 12 5 St. Louis 34 3 6 3 2B- Blake (20), Furcal (18). RBI- Kemp 3 (59), Furcal 2 (29). LOB- Los Angeles 9, St Louis 6. SB- Kemp (22). CS- Blake (4). Los Angeles in h r-er bb so era Kuroda 6.0 4 2-2 0 5 4.44 Mota 1.0 2 1-1 0 0 3.04 Kuo 1.0 0 0-0 2 2 4.50 McDonald (3-2) 1.0 0 0-0 0 0 5.18 Broxton (sv 4) 1.0 0 0-1 0 0 2.83 T- 3:23. Att- 43,263.