SEATTLE -- Edwin Diaz has been outstanding this season as the Mariners' closer and is on pace for a club-record 81 appearances and 60 saves, thanks in large part to the number of close games his team has played.

The hard-throwing right-hander was at it again on Wednesday, striking out the side in the ninth to finish off Seattle's 3-2 victory over the Giants for his MLB-leading 38th save in his 51st outing, which is tied for the most in the Majors.

Diaz's impact has been evident, but as the Mariners fight to land their first postseason berth since 2001, the question will be: How much work is too much for the 24-year-old fireballer?

The Mariners' record for appearances in a season is 78 by Ed Vandeberg, when he went 9-4 with a 2.37 ERA with five saves while racking up 76 innings as a 23-year-old rookie in 1982.

Vandeberg wasn't a closer, but he proved durable throughout his seven-year MLB career, pitching 68 games with a 3.36 ERA the following season, converting to a part-time starter in 1984 and bouncing back with another 76-appearance season in his final year with Seattle in '85.

Diaz certainly won't break any MLB records for usage. There have been 99 pitchers who have made more than 80 appearances in a season, topped by the remarkable 106 outings of Mike Marshall in 1974 with the Dodgers.

Many of the most-used relievers weren't closers who pitch in the highest-leverage situations each time out, but Francisco Rodriguez threw in 76 games in 2008 when he set the MLB record of 62 saves at age 26, and he continued on for a strong 16-year career.

Diaz pitched in 66 games last year while saving 34 games in his first full season as a closer. For his part, the youngster says he's feeling fine physically with two months remaining in the regular season.

"I feel great," Diaz said. "I work hard with my arm and body to feel good. I'm in good shape right now."

Coming off the All-Star break, Diaz certainly is fresh now. He's pitched just three times over the last two weeks, and Mariners manager Scott Servais says that should ease any concerns of overuse at this point.

"We had a streak where we won eight games in a row or whatever and he pitched in five or six of those. That's a little bit different," Servais said. "That's when you get more cautious and more worried about it. He's had some downtime.

"I'm really not that concerned about it. I think at the end of the year you look up, and what, is he going to pitch in 80 games? Is he going to pitch in 70 games? I don't know. But I hope he pitches in a lot, because that means we're in a good spot."

Servais believes Diaz benefits both from a durable arm and his ability to pitch efficiently this season. He's averaged 16.4 pitches per appearance and has been used in just two four-out saves, compared to seven multi-inning appearances last season.

Some fans question using Diaz in a "non-save" situation in a tie game in the ninth inning or beyond at home, when no save is possible since the home team can't take the lead at that point in order to record the statistic. But that is the same way nearly every closer in baseball is used.

Diaz took the loss in such a situation in Tuesday's 4-3 defeat to the Giants, but only because of a throwing error and unearned run.

"Eddie hasn't had the greatest of luck, and the numbers maybe don't look that great when he's in the ninth inning of a tie game, but you're trying to extend the game, you're trying to give your offense one more shot around, you put your best reliever that you have available out there," Servais said. "I certainly believe it. I think 100 percent of the managers in this game believe it."

Bottom line is, that the Mariners know they have a potent weapon in Diaz and will bring him in whatever situation best helps win games, as long as they feel he's healthy and not being overworked.

"When Eddie Diaz is available and I have a chance to pitch him, I'm going to pitch him," said Servais.

Altavilla advancing

Right-handed reliever Dan Altavilla , who has been sidelined six weeks with a strained elbow, extended his flat-ground throwing to 120 feet on Wednesday and is progressing now toward getting on the mound for a bullpen session on Aug. 3 if everything continues on schedule.

"It's feeling good is the main thing," said Altavilla. "It's been a lot of sitting around and it's really slow just watching, but I'm excited to eventually get back into games and contribute again. I've been patient, but now it's starting to get closer and I want to get back out there."

Greg Johns has covered the Mariners since 1997, and for MLB.com since 2011. Follow him on Twitter @GregJohnsMLB.