San Francisco Giants First-Place Eliminiation Scenario
San Francisco must win 5 more games (71 total) to avoid elimination from first place.
Here is a scenario in which San Francisco can finish in first place with 71 wins.

To construct the scenario, we start with the current standings in the division:
Team             W	L	GL	PCT	GB
San Francisco    66	39	57	0.629	0.0
Los Angeles      64	43	55	0.598	3.0
San Diego        61	47	54	0.565	6.5
Colorado         46	60	56	0.434	20.5
Arizona          33	73	56	0.311	33.5

Next, we show how the remaining series of games plays out in the scenario:

Arizona wins 0 games against Colorado and loses 6.
Arizona wins 6 games against Los Angeles and loses 0.
Arizona wins 10 games against San Diego and loses 0.
Arizona wins 9 games against San Francisco and loses 0.
Arizona wins 0 games agains teams outside the division and loses 0.

Colorado wins 6 games against Arizona and loses 0.
Colorado wins 6 games against Los Angeles and loses 0.
Colorado wins 3 games against San Diego and loses 0.
Colorado wins 10 games against San Francisco and loses 0.
Colorado wins 0 games agains teams outside the division and loses 0.

Los Angeles wins 0 games against Arizona and loses 6.
Los Angeles wins 0 games against Colorado and loses 6.
Los Angeles wins 7 games against San Diego and loses 2.
Los Angeles wins 0 games against San Francisco and loses 3.
Los Angeles wins 0 games agains teams outside the division and loses 0.

San Diego wins 0 games against Arizona and loses 10.
San Diego wins 0 games against Colorado and loses 3.
San Diego wins 2 games against Los Angeles and loses 7.
San Diego wins 8 games against San Francisco and loses 2.
San Diego wins 0 games agains teams outside the division and loses 0.

San Francisco wins 0 games against Arizona and loses 9.
San Francisco wins 0 games against Colorado and loses 10.
San Francisco wins 3 games against Los Angeles and loses 0.
San Francisco wins 2 games against San Diego and loses 8.
San Francisco wins 0 games agains teams outside the division and loses 0.

Combining the current standings with the wins and losses from the scenario results in the following final standings:
Team             W	L	PCT	GB
San Francisco    71	91	0.438	0.0
Colorado         71	91	0.438	0.0
Los Angeles      71	91	0.438	0.0
San Diego        71	91	0.438	0.0
Arizona          58	104	0.358	13.0


Next, we explain why San Francisco cannot win the division with fewer than 71 wins.

There are a total of 22 games left in the following series of games between teams in the National League West:
Los Angeles      vs. San Diego        9 games
Los Angeles      vs. San Francisco    3 games
San Diego        vs. San Francisco    10 games

For each team listed above, the table below shows the current number of wins in the (W) column.
The next column shows the maximum number of its remaining games that each team can win assuming that
SanFrancisco finishes in first place with a total of 70 wins.

Team             W	Max Additional Wins
Los Angeles      64	70 - 64 = 6
San Diego        61	70 - 61 = 9
San Francisco    66	70 - 66 = 4
Total            191	19

Since the total of the Max Additional Wins column is less than 22, it is not possible for SanFrancisco to win the division with 70 (or fewer) total wins.