SAN DIEGO — Maybe the San Francisco Giants made a devil's bargain for all those baseballs that Barry Bonds pounded over the palm trees at old Jack Murphy Stadium.

Or maybe the San Diego Padres have an airtight scouting report on the Giants, and their pitchers are following it to the letter.

Or maybe fish tacos enhance performance.

Whatever the reason, the Giants simply cannot beat their thrifty neighbors to the south. There comes a point when frustration becomes farce, but nobody was laughing after Monday night's 3-1 loss at Petco Park.

It bears repeating: the Giants are 0-7 against the Padres and 21-9 against everyone else.

Chase Headley hit a tiebreaking single off Matt Cain in the fifth inning, and the Giants were unable to rally. Their offense tallied just four hits against left-hander Clayton Richard and two relievers.

Every Giants mistake is a backbreaker against the Padres, and it was no different this time.

Cain was too aggressive with an 0-2 fastball that Adrian Gonzalez pounded for a solo home run in the first inning. After Headley put the Padres ahead, they added a run in the seventh when Sergio Romo plunked Kyle Blanks with the bases loaded.

Blanks, by the way, is stuck in an 0-for-26 rut with 13 strikeouts.

The tally is nearly as woeful for the Giants: nine runs in seven losses.

And in case you were wondering, since 1969, when the Padres sprang into being, neither team has swept a season series from the other. The Giants lost 11 of 13 to the Padres in 1996; they won 10 of 13 in '93. And thanks largely to a torrent of Bonds home runs, the Giants destroyed the Padres for a 14-5 record each season from 2001-03.

As if it mattered, the Giants entered this series as the hot team. While they were sweeping the Houston Astros last weekend, the Padres fell cold while losing three games at home to the Los Angeles Dodgers.

The Dodgers won Sunday afternoon despite getting just two hits.

The Giants doubled that. They managed a run, too, when Pablo Sandoval, Bengie Molina and Juan Uribe collected singles in the fourth inning.

But San Diego had the last answer, and it wasn't too surprising that the peskiest of Padres, David Eckstein, was at the center of it. He reached on a single that glanced off third baseman Sandoval, moved up on a one-out walk to Gonzalez and scored from second base when Headley punched his single to right field.

In Cain's previous start, he chastised himself for giving up run-scoring hits to Yorvit Torrealba on a pair of 0-2 pitches. He regretted another in the first inning when he missed over the plate while giving up Gonzalez's eighth home run.

But Cain learned other lessons. With Friday's baserunning clinic fresh in his mind, he varied his delivery and caught Will Venable jumping too quickly off first base.

The Giants had the tying runs on base in the eighth after setup man Mike Adams issued two-out walks to Andres Torres and Sandoval. But Molina firmly grounded out to strand both runners.

Closer Heath Bell's ninth inning was interrupted twice when fans ran onto the field. But after giving up a leadoff double to Aubrey Huff, he struck out Uribe and pinch hitter Eugenio Velez. Nate Schierholtz flied out to end it.

The Giants thought they caught a break before the first pitch, when the Padres put Scott Hairston on the disabled list with a strained hamstring. Hairston has crushed the Giants for 11 home runs and 25 RBIs in 180 at-bats, with much of the damage coming in close and late situations.

But this season, the Padres have no shortage of heroes against the Giants.